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Implications of new fault slip rates and paleoseismologic data for constancy of seismic strain release and seismic clustering in the eastern California shear zone

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Implications of new fault slip rates and paleoseismologic data for constancy of seismic strain release and seismic clustering in the eastern California shear zone

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Content IMPLICATIONS OF NEW FAULT SLIP RATES AND PALEOSEISMOLOGIC DATA
FOR CONSTANCY OF SEISMIC STRAIN RELEASE AND SEISMIC CLUSTERING
IN THE EASTERN CALIFORNIA SHEAR ZONE

by
Plamen Nikolov Ganev

________________________________________________________________________

A Dissertation Presented to the
FACULTY OF THE USC GRADUATE SCHOOL
UNIVERSITY OF SOUTHERN CALIFORNIA
In Partial Fulfillment of the
Requirements for the Degree
DOCTOR OF PHILOSOPHY
(GEOLOGICAL SCIENCES)

May 2011

Copyright 2011 Plamen Nikolov Ganev
ii

DEDICATION

In memory of my dad, Nikola Ganev, who elicited my scientific curiosity and taught me
how to always work hard in order to achieve my dreams.

iii

ACKNOWLEDGMENTS
Five years ago, naïve about the world and still in college, I found myself in the
office of Professor James Dolan talking about the endless possibilities that I could have if
I were to become a Ph.D. student. I always knew that I wanted to attain a Ph.D. degree in
one of the natural sciences, but after talking to James I knew I wanted to do it in one of
the leading schools in California, with one of the leading experts in active tectonics. The
decision was easy, and every time James and I have gone into the field or engaged into
scientific discussions, I have been reminded of how fortunate I am to be getting such a
high-level education. Although fun, and I do not refer here to James’ ―jokes‖, the road
has certainly been bumpy along the way, but James’ ability to see ―the big picture‖ and
encourage me to finish what I have started, has made this journey priceless. I am thankful
for every bit of knowledge that James has shared with me in order not only to make me a
better scientist, but a better person as well. In addition to James, a number of other people
have contributed directly and indirectly, consciously and unconsciously to this
dissertation and their recognition, in no particular order, is well-deserved bellow.
I am indebted to the members of my Ph.D. qualifying exam and dissertation
committees: Professors James Dolan, Kurt Frankel, Greg Davis, Thieo Hogen-Esch,
Steve Lund (Ph.D. qualifying exam committee member), and Charlie Sammis (Ph.D.
qualifying exam committee member). Each one of them has continuously challenged,
guided, and encouraged me how to best ―navigate‖ through the tumultuous waters of
science. Kurt Frankel, especially, has spent much more time discussing geochronology,
iv

geology, life in graduate school, and life in general, than he might have ever wanted, for
which I am extremely thankful. I appreciate his hospitality during my visits to Atlanta,
GA and all the arrangements he made for me to be able to work all those late nights at the
Georgia Institute of Technology. James Dolan, Charles Sammis, and Barbara Grubb
allowed me to grow as an educator and made my teaching assistant experience a great
pleasure. Kimberly Blisniuk, Robert Finkel, Kurt Frankel, Mike Oskin, Lewis Owen, and
Sally McGill were enthusiastic collaborators who provided unforgettable moments in the
field as well as thoughtful reviews of my manuscripts. Thought-provoking discussions
with Lisa Alpert, Whitney Behr, Kimberly Blisniuk, Chris Crosby, Greg Davis, James
Dolan, Austin Elliott, Kurt Frankel, Erik Frost, Eldon Gath, Ben Haravitch, Jeff Hoeft,
Ken Hudnut, Ozgur Kozaci, Lorraine Leon, Steve Lund, Chris Madden, Lee McAuliffe,
Sally McGill, Mike Oskin, Lewis Owen, John Platt, Tom Rockwell, Dylan Rood, Trevor
Thomas, Jeremy Zechar, and many others helped shape my thoughts on geochronology,
paleoseismology, active tectonics, and landscape evolution. Katelyn Carman, Austin
Elliott, Kurt Frankel, Erik Frost, Ben Haravitch, Ozgur Kozaci, Lorraine Leon, Lee
McAuliffe, Sally McGill, Miyu Sato, Trevor Thomas, and Jason Yun had to endure with
me the 110+ °F summer heat of the Mojave Desert and the 60+-mile-an-hour strong
winds of the Fish Lake Valley while assisting me in the field by digging soil pits,
collecting and carrying rock samples, and mapping faults.
My officemates, Kurt Frankel, Ozgur Kozaci, Lorraine Leon, Erik Frost, and later
Ben Haravitch and Lee McAuliffe, provided me with endless entertainment outside of my
v

Ph.D. research by making sure I take enough breaks for coffee, gym work-outs,
racquetball, and ping-pong games. Commiserating together the ―lives of Ph.D. students‖
over delightful lunches and afternoon coffee, Lisa Alpert and Whitney Behr were always
there when I needed someone to talk to. John McRaney, and his magic skills, made sure
that I continue forward with my research by providing me with continuous funding
throughout my tenure at USC. John Yu made sure that I always have the latest upgrades
to my software that enabled me to do rigorous analysis of my data, while Cynhia Waite
made sure I signed all the correct forms to keep me on track to graduate. Vardui Ter-
Simonian and Stanley Wright were always there when I needed their help with figuring
out class schedules and department vehicle requests.
The friendships that I have developed during graduate school are countless and I
cherish each and every one of them. Kurt Frankel, a former officemate, field assistant,
Ph.D. qualifying exam and dissertation committee member, and a geochronology guru,
has become a friend that I can call any time of the day and pester him with my questions.
Lisa Alpert, Whitney Behr, Frances Cooper, Austin Elliott, Erik Frost, Ben Haravitch,
Ozgur Kozaci, Lorraine Leon, and Lee McAuliffe are friends who know best the good
and bad times of graduate school, and I am grateful to have shared those moments with
them. Lee McAuliffe made sure that not only was I in good shape by going on 2-hour
long runs through Santa Monica on Saturday mornings, but that I was also well-fed by
going out to dinners with him, Alison Koop, and Katelyn Carman.
vi

Several people deserve special mention. If it weren’t for Professor Jan Vermylie
from Whittier College and her out-of-this-world enthusiasm for rocks, I might have never
become interested in geology in the first place. By putting me through ―geology boot
camp‖, where I was expected to dust all of the rock collections during my first semester
in college, she clearly tested my determination. My interest was further captured by
Professor An Yin’s willingness to share everything he knew with me during two summer
internships in 2004 and 2005 on the UCLA campus. However, none of this would have
been possible if it were not for Jerald Medway and his pure desire to make the world a
better place. He has provided me not only with the opportunity and guidance how to be
successful in a foreign society, but with a life-long friendship built upon, among other
things, the common thread of world travel. Ellen Medway, besides keeping me strong
with endless supplies of turkey jerky, was always there to listen to me complain about
little things over dinners, while Alexandra, Lynda and Stan Saperstein provided me with
the much appreciated family-love away from my family. Nadine and Harold Davidson
showed me how to care and love about something much bigger than oneself, and they
instilled their love in me for USC and the Trojan Family. Leslie and John Carman’s
support made my life much easier, and I greatly appreciate the many times they provided
me with Chinese chicken breasts, banana nut bread, and Starbucks gift cards. My mother
Kirilka Ganeva, sister Rumyana Ganeva, and the rest of my family have never once
questioned my decisions to (1) go abroad for college, and (2) spend so many years in
school. Although we have seen each other once a year for the past nine years, their love,
vii

support, encouragement, and friendship are felt each and every day some ~7,000 miles
away. My father, Nikola Ganev, who cannot share this milestone with me, taught me at
an early age the important life-lessons of hard work, dedication, and focus, and I will
carry these invaluable qualities with me the rest of my life. And last, but certainly not
least, Katelyn Carman has provided me with unconditional love, support, encouragement,
friendship and laughter. Her willingness to put up with me and my crazy ways of doing
things for the past seven years is simply remarkable, and I cannot express how happy I
am to have her by my side. She is always willing to nag me about my sitting posture, but
I appreciate her ―mad‖ physical therapy skills and honest concern about my well-being.
Lastly, none of the work presented in this dissertation would have been possible
without the financial support of the National Science Foundation, NASA, the Southern
California Earthquake Center, Georgia Institute of Technology, and the University of
Southern California Graduate School and Department of Earth Sciences.
This dissertation includes parts of the following manuscripts:

1) Ganev, P.N., Dolan, J.F., Frankel, K.L., and Finkel, R.C., 2010, Rates of
extension along the Fish Lake Valley fault and transtensional deformation
in the Eastern California shear zone-Walker Lane belt: GSA Lithosphere,
v. 2, no. 1, p. 33-49, doi:10.1130/L51.1.

2) Ganev, P.N., Dolan, J.F., Blisniuk, K., Oskin, M., and Owen, L.A., 2010,
Paleoseismologic evidence for multiple Holocene earthquakes on the
Calico fault: Implications for earthquake clustering in the Eastern
California shear zone: GSA Lithosphere, v. 2, no. 4, p. 287-298,
doi:10.1130/L82.1.

viii

3) Ganev, P.N., Dolan, J.F., McGill, S.F., and Frankel, K.L., in review, Constancy of
geologic slip rate along the central Garlock fault: Implications for strain
accumulation and release in southern California: Geophysical Journal
International.

The co-authors listed above shared data, assisted with field work, and helped to supervise
the published research results.

ix

TABLE OF CONTENTS

Dedication ii

Acknowledgments iii

List of Tables xii

List of Figures xiii

Abstract xvi

Chapter 1: Introduction 1
1.1 Introduction 1
1.2 Eastern California Shear Zone and Garlock Fault 2
1.2.1 Fish Lake Valley Fault System 6
1.2.2 Garlock Fault System 7
1.2.3 Calico Fault System 9
1.3 Light Detection and Ranging (LiDAR) Mapping 10
1.4 Geochronology Methods 11
1.4.1 Beryllium-10 Terrestrial Cosmogenic Nuclide (TCN) 11
Geochronology
1.4.2 Optically Stimulated Luminescence (OSL) 13
Geochronology
1.5 Research Implications 16

Chapter 2: Rates of Extension Along the Fish Lake Valley Fault and 18
Transtensional Deformation in the Eastern California
Shear Zone-Walker Lane Belt
2.1 Abstract 18
2.2 Introduction 19
2.3 Death Valley – Fish Lake Valley Fault Zone 23
2.4 Terrestrial Cosmogenic Nuclide Geochronology 26
2.4.1 Perry Aiken Creek Fan Age 30
2.4.2 Wildhorse Creek Fan Age 32
2.4.3 Furnace Creek and Indian Creek Fan Ages 33
2.5 Geomorphic Analysis of Normal Fault Scarps 33
2.5.1 Furnace Creek 42
2.5.2 Wildhorse Creek 43
2.5.3 Perry Aiken Creek 45
2.5.4 Indian Creek 47
x

2.6 Summary of Rate Data along the Fish Lake Valley Fault 50
2.7 Discussion 52
2.7.1 Geodetic Versus Geologic Rates of Extension 54
2.7.2 Strain Transfer at the Eastern California 57
Shear Zone – Walker Lane Transition
2.8 Conclusions 63

Chapter 3: Constancy of Geologic Slip Rate Along the Central 65
Garlock Fault: Implications for Strain Accumulation
and Release in Southern California
3.1 Abstract 65
3.2 Introduction 66
3.3 Active Tectonics of the Garlock Fault: Previous Work 68
3.4 Summit Range Study Area 73
3.4.1 Fault Displacement 78
3.4.2 TCN Geochronology 83
3.4.3 TCN Results 84
3.4.3.1 Qf3 84
3.4.3.2 Qoa 89
3.5 Latest Pleistocene-Earliest Holocene Fault Slip Rate 91
3.5.1 Minimum Rate Based on Fan Abandonment Age 91
3.5.2 Possible Maximum Rate Based on Paleoclimate 91
Considerations
3.6 Discussion 93
3.6.1 Geologic Slip Rate Comparisons From 93
the Garlock Fault
3.6.2 Geologic VS. Geodetic Slip Rate Comparisons 96
from the Garlock Fault
3.7 Conclusions 99

Chapter 4: Paleoseismologic Evidence for Multiple Holocene 101
Earthquakes on the Calico Fault: Implications for
Earthquake Clustering in the Eastern California Shear Zone
4.1 Abstract 101
4.2 Introduction 102
4.3 Site Description 104
4.4 Paleoseismic Trenching 107
4.5 Age Control 110
4.6 Interpretation of Paleo-Surface Ruptures 115
4.6.1 Event 1 115
4.6.2 Event 2 120
xi

4.6.3 Event 3 121
4.6.4 Event 4 123
4.7 Measurement of Small-Scale Geomorphic Offsets 125
4.8 Discussion 129
4.9 Conclusions 134

Chapter 5: Conclusions 135
5.1 Summary 135
5.2 Constancy of Seismic Strain Release 135
5.2.1 Constancy of Seismic Strain Release in 135
the Northern Eastern California Shear Zone
5.2.2 Constancy of Seismic Strain Release on the 137
Garlock Fault
5.3 Spatial Variations in Slip Rate Along the Fish Lake 138
Valley Fault
5.4 Seismic Clustering in the Southern Eastern California 139
Shear Zone

References 140

Appendices 160
Appendix A: Fish Lake Valley Fault Scarp Profiles and 160
Displacement Measurements
Appendix B: Paleoseismologic Trenching and Geochronology of 171
the Calico Fault
B1 Paleoseismologic Trenching 171
B2 Optically Stimulated Luminescence (OSL) 174
Geochronology
B3 Additional Photo Logs of the Paleoseismic Trenches on 178
the Calico Fault

xii

LIST OF TABLES

Table 2.1: Analytical Results of Terrestrial Cosmogenic Nuclide 29

10
Be Geochronology for the Wildhorse Creek and
Perry Aiken Creek Alluvial Fans in Fish Lake Valley

Table 2.2: Extension Rates for the Four Study Sites Resolved 51
Toward N65°E

Table 3.1: Analytical Results of Terrestrial Cosmogenic Nuclide
10
Be 88
Depth Profile Geochronology for the Summit Range Site

Table 4.1: Summary of OSL Dating Results Extracted From Sediment, 111
Sample Locations, Radioisotopes, Concentrations, Moisture
Contents, Total Dose-Rates, D
E
Estimates, and Optical Ages

Table 4.2: Summary of Measured Displacements along the Calico Fault 128
of the Eastern California Shear Zone

Table A1: Measured Vertical and Calculated Horizontal Offsets from 168
Topographic Profiles

xiii

LIST OF FIGURES

Figure 1.1: Index Map of the Eastern California Shear Zone 5

Figure 2.1: Fault Map of the Northern Eastern California Shear Zone 22

Figure 2.2: Fish Lake Valley Fault Map with Study Sites 24

Figure 2.3: Field Photographs of Sampled Boulders for
10
Be Geochronology 28

Figure 2.4: Probability Density Functions of
10
Be Ages 31

Figure 2.5: Selected Topographic Profiles Across Alluvial-fan Surfaces 35

Figure 2.6: Vector Resolutions for Horizontal Extension 37

Figure 2.7: LiDAR-derived Image of Furnace Creek 38

Figure 2.8: LiDAR-derived Image of Wildhorse Creek 39

Figure 2.9: LiDAR-derived Image of Perry Aiken Creek 40

Figure 2.10: LiDAR-derived Image of Indian Creek 41

Figure 2.11: Retrodeformed Wildhorse Creek and Perry Aiken Creek Maps 49

Figure 2.12: Rates of Extension in the Northern Eastern California 56
Shear Zone

Figure 2.13: Fault Model for Slip Transfer between the Eastern California 62
Shear Zone and Walker Lane Belt

Figure 3.1: Index Map of the southern Eastern California Shear Zone and 70
Garlock Fault

Figure 3.2: Map of the central part of the Garlock fault 74

Figure 3.3: Annotated LiDAR Image, Aerial photograph, and Topographic 75
Map of the Summit Range Site

xiv

Figure 3.4: Quaternary Map and Retrodeformed Image of 77
the Summit Range Site

Figure 3.5: Panoramic View Looking South Towards the Summit Range 79

Figure 3.6: View Overlooking the Summit Range Site 80

Figure 3.7: Slip Restorations of Various Amounts 82

Figure 3.8:
10
Be Cosmogenic Nuclide Depth Profiles From Qf3 87
and Qoc Deposits

Figure 3.9: Garlock Fault Slip Rate Map 94

Figure 3.10: Compilation of Slip Rates from the Garlock Fault on 97
a Time VS. Slip-Rate Graph.

Figure 4.1: Fault Map of the Southern Eastern California Shear Zone 103

Figure 4.2: Aerial Photograph of the Calico Fault Surface Expression 105

Figure 4.3: Photograph of the Calico Fault Trace 106

Figure 4.4: Simplified Fault Trench Logs of the Calico Fault 108

Figure 4.5: Detailed Photograph Logs of the Calico Fault 109

Figure 4.6: Composite Stratigraphic Column 113

Figure 4.7: Sediment Accumulation Rate Curve 114

Figure 4.8: Geomorphic Analysis Map 127

Figure 4.9: Composition of Paleoearthquake Ages from the Calico Fault 130
and Compilation of Seismic Moment Release Data in
the Southern Eastern California Shear Zone

Figure A1: Complete List of Analyzed Topographic Profiles from 161
the Fish Lake Valley Fault

Figure A2: Restoration of Right Lateral Offset at Perry Aiken Creek Site 167
xv

Figure B1: Detailed Photo Logs Between Meters 8-12 and 21-26 from 178
the Northern Wall of the Northern Trench from the Calico Fault

Figure B2: Additional Event Horizon Evidence from the Calico Fault 179

Figure B3: Photomosaic Logs of the Trench Walls from the Calico Fault 180

xvi

ABSTRACT
The spatial and temporal strain accumulation and release patterns of faults remain
an enigma, which has received an enormous amount of attention from geologists.
Although the faults of the Eastern California shear zone (ECSZ), including the Garlock
fault, are some of the most studied in the world, we still have only limited understanding
of their role in the Pacific-North America plate boundary deformation. Geodetic models
suggest that the right-lateral northwest-southeast striking ECSZ is the main fault system
accumulating strain east of the San Andreas fault, while the left-lateral almost east-west
striking Garlock fault has low strain accumulation rates. More geochronologically
constrained slip rates are needed from the faults of the ECSZ and Garlock fault in order
to determine whether strain storage and release are constant in this region. As part of this
dissertation, I focused on several locations along the Garlock fault in southern California,
and the Fish Lake Valley Fault (FLVF) in the northern part of the ECSZ, where I used
Light Detection and Ranging (LiDAR) digital topographic data to measure normal fault
scarps and restore offset alluvial fans to their pre-faulting positions. Combining those
restorations with cosmogenic
10
Be geochronology of the offset deposits, I was able to
determine slip rates along the FLVF and Garlock fault systems.
Besides the major right-lateral component of slip, the Fish Lake Valley fault also
exhibits a normal slip component. Offset scarp measurements combined with cosmogenic
nuclide geochronology from four sites yield late a Pleistocene-Holocene horizontal
extension slip rate that ranges from 0.1 ± 0.1 mm/yr to 0.7 +0.3/-0.1 mm/yr. Comparison
xvii

of this slip rate with geodetic measurements of ~1 mm/yr of extension across the northern
ECSZ indicates that the FLVF accommodates approximately half of the current rate of
regional extension. When summed with published rates of extension for faults at the same
latitude, the FLVF data indicate that long-term geologic deformation rates are
commensurate with short-term geodetic extension rates.
Combining an offset measurement of an incised channel across the central
Garlock fault with a modeled
10
Be surface age, yield a late Pleistocene-Holocene slip rate
of 5.3 +1.0/-2.0 mm/yr, and a maximum rate of ~6.6 ± 1.2 mm/yr. This rate is similar to
previously published geologic slip rates to the west and east of the study site, but it is at
least twice as fast compared to reported geodetic strain accumulation rates along the
Garlock fault. The similarities, in terms of channel offsets and ages of the incised
surfaces between multiple sites along the fault, are indicative of climatically controlled
aggradational and degradational events throughout time that are regional in extent. In
addition, these data suggest that, as proposed before, a strain transient could be present
along the Garlock fault and strain accumulation and release rates have not remained
constant through time.
Such a strain transient has also been proposed for the ECSZ south of the Garlock
fault. As part of this dissertation, I also studied the paleoseismic record of the Calico
fault, the fastest slipping fault in the southern ECSZ. Evidence of surface ruptures
between 0.6-2-0 ka, 5.-5.6 ka, 5.6-6.1 (or possibly 7.3) ka, and 6.1 (or 7.3) to 8.4 ka along
the Calico fault, coincide with similar clusters elsewhere in southern ECSZ. These data
xviii

strongly reinforce earlier suggestions that earthquake recurrence in the ECSZ is highly
clustered in time and space.
1

CHAPTER 1:
Introduction

1.1 Introduction
One of the most exciting and heavily-debated topics within the Earth Sciences
community is whether strain accumulation and release are temporally and spatially
constant (or non-constant). In order to understand how strain is distributed in time and
space, a sufficient amount of slip rate data over different time scales, from short-term
(10
1
yrs.) geodetic to longer-term (10
6
yrs.) geologic scale, are needed. Such data are
extremely important if we want to better understand the behavior of faults.
Studying this complex fault behavior requires a multidisciplinary approach that
involves the analysis of high-resolution digital topographic data coupled with the latest
geochronologic techniques. Furthermore, in order to understand whether strain release is
periodic, i.e. whether earthquakes occur in clusters through time, a paleoseismic fault
analysis is also required. This dissertation comprises research that uses such a
comprehensive approach and focuses on faults that are part of the Eastern California
shear zone (ECSZ), an important component of the Pacific-North America plate
boundary. Specifically, my research was two-fold and focused on (1) mapping,
displacement restoration, and age determination of offset landforms along the Fish Lake
Valley Fault (FLVF) and Garlock fault by combining high-resolution Light Detection and
Ranging (LiDAR) topographic data with
10
Be terrestrial cosmogenic nuclide (TCN)
geochronology, and (2) studying the earthquake history of the of the Calico fault through
fault trenching and optically stimulated luminescence (OSL) geochronology.
2

The slip rate study on the FLVF was proposed as a follow-up to Frankel’s (2007)
PhD work on that fault, and it was meant to provide a complete view of the cumulative
extension rates of the major faults of the ECSZ north of the Garlock fault over geodetic to
geologic time scales. Similarly, the Garlock fault slip rate study aimed to provide a better
understanding of the long-term geologic slip rates and how they compare to the short-
term strain accumulation rates. Comparisons of the geologic and geodetic slip rates
allowed me to determine whether strain storage and release have been constant over the
late Pleistocene-Holocene time scale, or whether a strain transient is present as proposed
before by others (e.g., Peltzer et al., 2001). In addition, I also studied the paleoseismic
record of the Calico fault, the fastest slipping fault of the ECSZ south of the Garlock
fault, in order to determine whether seismicity in that region has occurred in clusters
during the Holocene epoch as proposed by Rockwell et al. (2000).

1.2 Eastern California Shear Zone and Garlock Fault
The Eastern California shear zone is an evolving fault system east of the San
Andreas fault (SAF) that accommodates ~20%–25% (9–10 mm/yr) of Pacific–North
America plate-boundary deformation (e.g., Dokka and Travis, 1990b; Humphreys and
Weldon, 1994; Hearn and Humphreys, 1998; Thatcher et al., 1999; Dixon et al., 2000,
2003; McClusky et al., 2001; Miller et al., 2001; Bennett et al., 2003; Faulds et al., 2005;
Wesnousky, 2005a, 2005b; Frankel et al., 2007a). The Eastern California shear zone
extends northward for almost 500 km from the San Andreas fault near Palm Springs, CA
through the Mojave Desert and along the eastern side of the Sierra Nevada. In the Mojave
3

section of the shear zone, fault motion is primarily right-lateral, with a subordinate
component of north-south shortening, and slip is localized along several major north-
northwest–striking faults (Dokka, 1983; Bartley et al., 1990; Dokka and Travis, 1990a,
1990b; Schermer et al., 1996; Walker and Glazner, 1999; Glazner et al., 2002; Oskin et
al., 2007a, 2007b, 2008). North of the active left-lateral Garlock fault, motion is
accommodated on four major fault systems: the Owens Valley, Panamint Valley–Saline
Valley–Hunter Mountain, Death Valley–Fish Lake Valley, and Stateline fault zones
(Figure 1.1; e.g., Beanland and Clark, 1994; Lee et al., 2001, 2009a, 2009b; Oswald and
Wesnousky, 2002; Kylander-Clark et al., 2005; Bacon and Pezzopane, 2007; Frankel et
al., 2007a, 2007b, 2008a, 2008b; Guest et al., 2007; Kirby et al., 2008). Although these
faults have a predominant right-lateral slip component, they also have an extensional slip
component that is approximately perpendicular to the strike orientation.
The Garlock fault is the major fault system that separates the ECSZ into southern,
Mojave, section, and northern section. This left-lateral fault system, although not fully
understood, has been proposed to serve as: (1) conjugate shears along with the SAF and
Big Pine fault accommodating north-south compression and east-west extension (Hill and
Dibblee, 1953; McGill et al., 2009); (2) a transform fault accommodating differential
extension in the Basin and Range province relative to the Mojave block (Hamilton and
Myers, 1966; Troxel et al., 1972; Davis and Burchfiel, 1973); or (3) clockwise rotation of
blocks in the northeastern Mojave Desert contributes left slip to the Garlock fault
(Humphreys and Weldon, 1994; Guest et al., 2003).
4

As part of this dissertation, I focus on studies conducted along the Fish Lake
Valley fault in the northern ECSZ, the Garlock fault, and the Calico fault in the southern
ECSZ.

5

Figure 1.1 Map of Quaternary faults in the Eastern California shear zone.
Northwest-southeast striking faults have a predominant dextral slip; Garlock fault
is a sinistral fault. Faults shown in yellow, i.e. Fish Lake Valley-Death Valley fault
system, Garlock fault system, and Calico fault system were studied as part of this
dissertation. Faults are from the U.S. Geological Survey (USGS) Quaternary fault
and fold database. AHF – Ash Hill fault, ALF – Airport Lake fault, BF –
Blackwater fault, BLF- Bicycle Lake fault, CF – Calico fault, CLF – Coyote Lake
fault, CRF – Camp Rock fault, EPF – Emigrant Peak Fault, EVF – Eureka Valley
fault, DSF – Deep Springs fault, FLVF – Fish Lake Valley fault, FIF – Fort Irwin
fault, GF – Garlock fault, GLF – Goldstone Lake fault, HLF – Harper Lake fault,
HF – Helendale fault, HMSVF – Hunter Mountain-Saline Valley fault, LF –
Lenwood fault, LoF – Lockhart fault, NDVF – northern Death Valley fault, OVF –
Owens Valley fault, PVF – Panamint Valley fault, SAF – San Andreas fault, SNF –
Sierra Nevada frontal fault, SDVF – southern Death Valley fault, TF – Tiefort fault,
TMF – Tin Mountain fault, TPF – Towne Pass fault, WMF – White Mountains
fault.
6

1.2.1 Fish Lake Valley Fault System
The Fish Lake Valley fault, and its southern extent- the Death Valley fault, is the
fastest slipping fault system of the Eastern California shear zone, and it accommodates
most of the Pacific-North America plate motion east of the San Andreas fault. In the
northern part of the ECSZ, between latitude 37ºN and 38ºN, almost all dextral motion
between the stable Sierra Nevada block and North America is transferred onto the White
Mountains fault and the Fish Lake Valley fault (Frankel et al., 2007b). Space-based
geodetic studies (Savage et al., 1990; Bennett et al., 1997; Dixon et al., 2000; McClusky
et al., 2001; Dixon et al., 2003) have shown that the short-term (tens of years) slip rate on
the Death Valley and Fish Lake Valley faults is 3-8 mm/yr, while the total geodetic slip
rate on the ECSZ is 9-12 mm/yr (Dokka and Travis, 1990). GPS surveys (Savage et al.,
2001; Bennett et al. 2003) have also shown active extension on the predominantly dextral
faults north of the Garlock fault. Wesnousky’s (2005) observations, based on data
published earlier by Bennett et al. (2003), suggest an extensional slip rate of ~1 mm/yr
measured normal to the strike of the ECSZ (~N25ºW). As the single most active fault in
the northern ECSZ, the Fish Lake Valley fault has an extensional slip rate that can
account for nearly half the rate of northwest-directed shear-related extension between the
stable North American plate and the Pacific plate (Argus and Gordon, 1991; Dixon et al.,
1995).
Although numerous geologic studies have estimated the right-lateral slip rates on
the Fish Lake Valley and Death Valley fault systems (e.g., Brogan et al., 1991; Oldow et
al., 1994; Reheis and Sawyer, 1997; Klinger and Piety, 2001; Frankel et al., 2007a and b),
7

only a handful of them (e.g., Reheis and Sawyer, 1997; Klinger and Piety, 2001), have
investigated the extensional slip rates on this fault system. Therefore, I examined the
poorly understood intermediate- to long-term extension rates on the Fish Lake Valley
fault, and compared them to the geologic dextral slip rates and geodetic measurements of
strain accumulation.
1.2.2 Garlock Fault System
The Garlock fault, a major geologic and physiographic boundary between the
southwestern Basin and Range Provence to the north and the Mojave Desert to the south,
is one of the major strike-slip faults in Southern California. The left-lateral system
extends for ~250 km from the San Andreas fault to the west to the Death Valley fault,
and possibly east of it (Davis and Burchfiel, 1973; Plescia and Henyey, 1982), to the east.
It strikes northeasterly to the west, but changes its strike orientation more easterly
towards its eastern end. The total documented sinistral displacement is 48-64 km (Smith,
1962; Smith and Ketner, 1970; Davis and Burchfiel, 1973; Monastero et al, 1997), which
initiated some time between 17 Ma and 10 Ma (Burbank and Whistler, 1987; Loomis and
Burbank, 1988; Monastero et al., 1997; Frankel et al., 2008). The fault exhibits a
prominent left stepover in the vicinity of Koehn Lake and a ~15º change in strike south of
the Quail Mountains.
I adopt McGill and Sieh’s (1991) classification of the three fault segments in
which the Garlock fault can be divided: (1) western Garlock fault- west of the stepover at
Koehn Lake; (2) central Garlock fault- between the stepover at Koehn Lake and the Quail
Mountains; and (3) eastern Garlock fault- east of Quail Mountains. Each of the three
8

segments is not only geographically different, but geologically different as well. The
western Garlock fault has a relatively complex fault trace as it extends through the
southern Tehachapi Mountains where very limited offset geomorphic landforms are
preserved. In contrast, the central and eastern Garlock fault segments exhibit a simpler
fault trace with well-preserved sinistrally displaced incised channels and alluvial fans.
Due to national security reasons access to the eastern Garlock fault is limited as it is
located within the borders of the China Lake Naval Weapons Center. Therefore, I
focused my efforts on studying the easily-accessible and well-defined central Garlock
fault segment.
Reported late Pleistocene-Holocene slip rates on the Garlock fault have been
highly variable throughout time, from ~1 mm/yr (Smith, 1975) to ~11 mm/yr (Carter,
1980; 1982). Nevertheless, an emerging geologic slip rate of 5-7 mm/yr (Clark and
Lajoie, 1974; McGill, 1992; McGill and Sieh, 1993; Carter et al., 1994; McGill et al.,
2009) seems to be the consensus at present among many researchers. Such geologic slip
rates, however, are inconsistent with most geodetically derived slip rates on the Garlock
fault, which indicate left-lateral slip rates that are no more than half the geologic slip rates
(McClusky et al., 2001; Miller et al., 2001; Peltzer et al., 2001; Meade and Hager, 2005).
Instead, these geodetic studies suggest a predominant northwest-oriented, right-lateral
shear, i.e. eastern California shear zone, south and north of the Garlock fault. Such a
shear zone could be related to the temporal and spatial clustering of earthquakes along the
Garlock fault (Peltzer et al., 2001; Dolan et al., 2007), however what the relationship
9

between the Garlock fault and the rest of the northwest-oriented right-lateral faults of the
ECSZ remains unknown.
1.2.3 Calico Fault System
The Calico-Blackwater fault system is the longest in the Mojave section, i.e. the
section south of the Garlock fault, of the Eastern California shear zone. Recent studies
indicate a long-term slip rate for the Calico fault of 1.8 ± 0.3 mm/yr, averaged over the
past 57 ± 9 ka (Oskin et al., 2007, 2008). Although this is about one third of the total
geologic slip rate across the six major faults (i.e., Helendale, Lenwood, Camp Rock,
Calico-Blackwater, Pisgah, and Ludlow) that comprise the Mojave section of the ECSZ,
the paleoearthquake history of the Calico fault has not previously been documented.
A compilation of paleoseismologic data from the majority of the faults in the
Mojave section of the ECSZ, but not including the Calico fault, revealed that strain
release has been highly episodic over the past 12,000 years, with pronounced clusters of
earthquakes at ~ 8 to 9.5 ka, 5 to 6 ka, and during the past ~ 1,000-1,500 years (Rockwell
et al., 2000). The 1992 M
w
7.3 Landers and 1999 M
w
7.1 Hector Mine earthquakes are
the two most recent earthquakes of an ongoing, latest-Holocene cluster.
The lack of previous paleoseismic studies of the Calico fault thus leads to a
simple test of the clustering hypothesis proposed by Rockwell et al. (2000). Because the
Calico fault slips faster than other nearby faults, larger or more frequent earthquakes
should accommodate its slip. If regional clustering of earthquakes modulates fault-zone
activity in the Mojave Desert section of the ECSZ, then these earthquakes should fall into
the regional clustering time periods identified by Rockwell et al. (2000). Therefore, as
10

part of my dissertation, in chapter 4 I describe the results of a paleoseismologic trench
study and geomorphic analysis of offset features along the northern part of the Calico
fault, and discuss the implications of the results for earthquake behavior and seismic
hazard assessment in the southern Eastern California shear zone.

1.3 Light Detection and Ranging (LiDAR) Mapping
The use of LiDAR digital topographic data to analyze geomorphic features has
revolutionized the field of Neotectonics. Such data are used to create sub-meter
resolution digital elevation models (DEM) of the surface, which have replaced the
collection of low sun-angle aerial photos. One of the biggest advantages of DEMs is the
ease and efficiency by which one can artificially illuminate the surface by adjusting the
virtual sun angle (direction and azimuth) to discern subtle features of the landscape,
which have been unrecognized in the past. In addition, the DEMs have approximately a
decimeter vertical accuracy, and after processing the data in ArcGIS geospatial analysis
software topographic contour maps can be created. By utilizing the same software
program, multiple topographic profiles across fault scarps can be generated in a matter of
hours. This technique was very useful in Fish Lake Valley where I studied the extension
rate on the Fish Lake Valley fault. In addition, the high-resolution LiDAR-based DEMs
from the Garlock fault were extremely helpful in recognizing and mapping offset alluvial
deposits in the field, which otherwise would have been very hard to identify.
The LiDAR data of the Fish Lake Valley fault and Garlock fault were collected in
the fall seasons of 2005 and 2008, respectively, by the National Center for Airborne
11

Laser Mapping (NCALM), and are now publically available through
http://www.opentopography.org.

1.4 Geochronology Methods
I have utilized two main geochronology methods as part of the projects included
in this dissertation. For the studies on the Fish Lake Valley fault and Garlock fault I used
10
Be terrestrial cosmogenic nuclide (TCN) dating, while for the Calico fault study I used
optically stimulated luminescence (OSL) dating.
1.4.1 Berrylium-10 Terrestrial Cosmogenic Nuclide (TCN) Geochronology
Since it was first developed, cosmogenic nuclide exposure dating has undergone
major progress, and it has become a reliable technique in studying landscape evolution
(e.g., Gosse and Phillips, 2001; Hidy et al., 2010). Galactic cosmic rays penetrate the
atmosphere and irradiate minerals in rocks exposed at the Earth’s surface. This irradiation
causes four main terrestrial in-situ cosmogenic nuclides (TCN) to be produced:
10
Be,
14
C,
26
Al, and
36
Cl. Of the four TCNs
10
Be,
14
C, and
26
Al can be found in quartz
minerals, while
36
Cl accumulates in carbonates and basalts. The main assumptions
behind cosmogenic surface exposure dating is that (1) the dated rock samples were
deposited at, or near the surface, (2) they have remained at the surface since the time of
deposition, and (3) they had no prior exposure history. The concentration of cosmogenic
nuclides is, therefore, a function of the time the sample has been exposed to cosmic
radiation and the production rate of the nuclides over time. Although the production rate
depends on multiple variables, such as geomagnetic latitude, altitude, solar activity,
12

shielding, and time, we now have better constraints on the amount of radionuclide
production (Finkel and Sutter, 1993; Masarik and Reedy, 1995; Tuniz et al., 1998;
Masarik and Beer, 1999, Lal, 2000; Gosse and Philips, 2001; Muzikar et al., 2003; Hidy
et al., 2010).
10
Be and
26
Al are two of the nuclides whose production rates in quartz can
be estimated fairly accurately for any given latitude and altitude (Lal, 1991). The
concentration )) of in-situ cosmogenic nuclides originating at a depth ) below
the Earth’s surface for a certain period of time ) is represented by the formula:
) )

)

)
) (1)
where ) is the initial nuclide concentration (atoms/g) in the sample of interest at
depth, x, after an irradiation for a time period, t, λ is the disintegration constant of the
radionuclide (decays/year), ) is the production rate of the radionuclide, is defined as
the nuclide’s absorption coefficient (

), and ε is the erosion rate (cm/year). It is
generally assumed that the sample has no prior exposure history ( ) ), as well
as, where appropriate, the erosion rate is negligible ( ε=0). Therefore, this significantly
simplifies the formula on the right side of Equation 1 (Lal, 1991).
One important issue with cosmogenic nuclide dating is that some samples
collected from alluvial fan surfaces might have been exposed to cosmic radiation as part
of a different depositional sequence, and they now possess cosmogenic inheritance
(Hancock et al., 1999). It has been shown (e.g., Anderson et al., 1996; Hancock et al.,
1999) that such a problem can be resolved by using the depth-profiling strategy. A certain
number of cosmic rays penetrate through the top layers of the surface. The rate at which
nuclide production rates decrease with depth depends on the density of the rock layers.
13

Typically, the production rates decrease by

⁄ for every 50 cm increase in depth, and
thus cosmic radiation becomes insignificant by the time it reaches a depth of ~2 m (Gosse
and Philips, 2001. If the inheritance is consistent throughout the depth profile, the ages of
the samples should decrease exponentially (e.g., Equation 1). Therefore, the age of the
surface can be determined by plotting age vs. depth of samples on a graph, and
extrapolating the fitted curve upward to a depth of 0 m.
As mentioned earlier, I used
10
Be nuclide geochronology to constrain the ages of
offset deposits along the Fish Lake Valley and Garlock faults. The two fault systems are
located in areas with very limited precipitation, which makes them ideal for cosmogenic
nuclide sampling. In most cases erosion rates are negligible, and the sites that I selected
had distinctive offset geomorphic features whose surfaces could be dated. I collected
samples from quartz-bearing boulders (e.g., granites, granodiorites) that were initially
deposited and remained on the alluvial surfaces along the FLVF, whereas I used the
depth-profiling technique on the alluvial deposits along the Garlock fualt.
I collected and processed a total of 15 samples from two sites along the Fish Lake
Valley fault, and 24 samples from four pits along the Garlock fault. All samples were
prepared at Professor Kurt Frankel’s Cosmogenic Nuclide Laboratory at the Georgia
Institute of Technology, and dated at the Center for Accelerator Mass Spectrometry
(CALM) at Lawrence Livermore National Laboratory.
1.4.2 Optically Stimulated Luminescence (OSL) Geochronology
The optically stimulated luminescence (OSL) dating technique has been
developed within the past 20 years (Huntley et al., 1985; Berger, 1995; Wintle, 1997;
14

Aitken, 1998; Singhvi and Wintle, 1999). The underlying principle for this
geochronologic technique is that quartz and feldspar minerals are used as dosimeters
recording their exposure to ionizing radiation from the environment (Duller, 1996).
Luminescence measurements are used to estimate the ionizing radiation dose, or
equivalent dose (DE) measured in grays (Gy), which the sample has absorbed since the
last time of light exposure. Separate measurements are used to assess the rate at which the
sample was exposed to natural ionizing radiation from the environment. This rate is
known as the average dose rate over time (DR) measured in Gy/ka, where time is given
as ka (1000) but other units of time are also applicable. The formula used to calculate the
ages of the OSL samples is therefore:
) / (
) (
) (
ka Gy D
Gy D
ka Age
R
E
 (2)
The luminescence signal that is used to measure the equivalent dose of Quaternary
sediments is sensitive to light. An implicit assumption is made that when dating
sediments the constituent mineral grains were exposed to daylight while they were being
transported, and thus the luminescence signal they may have already had was removed.
As a result, the equivalent dose in those sediments is zero, and therefore the age of the
dated sample is zero (Equation 2). It is this last exposure to light that is dated by the OSL
technique. While the quartz and feldspar grains are buried, and hence not exposed to
light, they are exposed to ionizing radiation originating from the radioactive decay of
K
40
and the decay chains of Th
232
, and U
238
contained in the sediment itself, in addition
to a small component of radiation from cosmic rays (Huntley, 1985). These radioisotopes
15

interact with the crystalline structure of the quartz and feldspar minerals, freeing
electrons from their normal atomic sites. Some of the electrons become trapped at defect
sites within the crystal lattice where they can remain indefinitely on a geological time
scale (Huntley et al., 1985). The trapped electrons can be freed by the absorption of
visible photons through light exposure in laboratory conditions. The number of these
trapped and freed electrons, therefore, is the measure of the equivalent rate since the last
time the traps were emptied.
The range of OSL dating extends from recent decades (Madsen et al., 2005) to
~500 ka years ago (Olley et al., 2004; Watanuki et al., 2005). The lower age limit is
determined by the lower detection limit of the OSL signal, while the upper age limit
depends on the saturation region of the equivalent dose as well as the natural dose rate.
Higher age limits can be obtained for lower dose rates; however high dose rates of ~ 5
Gy/ka useful for dating up to ~ 100 ka are typical from the sands and silts from the
Mojave desert (Duller, 1996). The biggest concern when using the OSL dating technique
is whether the dated sample has been completely or partially bleached since its
deposition. Therefore, collecting multiple samples from each layer and cross-referencing
the ages of the samples provides a constraint on any reworked deposits.
I collected and processed 11 OSL samples from the paleoseismic trenches on the
Calico fault. The samples were collected in galvanized pipes that were 3 inches wide and
1 foot long. The tubes were individually hammered into the desired sediment layers,
while covering the back of the pipe with aluminum foil to protect any sun-light exposure
of the collected sediments. Once the entire length of the pipe penetrated the wall of the
16

trench, the sample tube was carefully extracted, wrapped in aluminum foil, and a sample
number was assigned. A bulk soil sample was also collected within a 25-cm radius of the
tube sample location. The bulk soil sample was used to analyze the moisture content, as
well as the natural dose rate of the targeted sediment layer. All samples were prepared
and dated at Professor Lewis Owen’s geochronology laboratory at the University of
Cincinnati, Ohio.

1.5 Research Implications
The following three chapters present research results previously published in
international, peer-reviewed journals [Ganev et al., 2010a (Chapter 2); Ganev et al., in
review (Chapter 3); and Ganev et al., 2010b (Chapter 4)]. Chapter 2 reports on the first
geochronologically determined extensional slip rate on the Fish Lake Valley fault, and
discusses the implications for constancy of strain accumulation and release in the
northern Eastern California shear zone. In addition, this chapter proposes a plausible
model which explains the distribution of slip among the active faults of the northern-most
ECSZ and Mina Deflection. A study on the determination of a geologic slip rate from the
central Garlock fault is presented in Chapter 3, and the implications of surface deposition
and channel incision processes in the Mojave desert are discussed. Chapter 4 focuses on a
paleoseismic study on the Calico fault, which tests the seismic clustering hypothesis
proposed by Rockwell et al. (2000).
A summary of the main findings of my research is included in the conclusions
section (Chapter 5) of this dissertation. By integrating TCN geochronology with the latest
17

LiDAR digital topographic data, I was able to provide new data that helped in the
analysis of spatial and temporal patterns of strain accumulation and release along some of
the major faults in the ECSZ. Additionally, I was also able to determine the earthquake
history on the fastest slipping fault in the southern ECSZ. Therefore, the results of my
research have direct implications for understanding lithospheric dynamics, fault zone
kinematics, and probabilistic seismic hazard analysis, not only within the Eastern
California shear zone, but for the Pacific-North America plate boundary as well.
Each chapter of the dissertation is designed to stand alone, and therefore the
amount of redundancy is unavoidable. For this, I apologize to the reader.

18

CHAPTER 2:
Rates of Extension along the Fish Lake Valley Fault and Transtensional
Deformation in the Eastern California Shear Zone-Walker Lane Belt

2.1 Abstract
The oblique-normal-dextral Fish Lake Valley fault accommodates the majority of
Pacific–North America plate-boundary deformation east of the San Andreas fault in the
northern part of the Eastern California shear zone. New rates for the extensional
component of fault slip, determined with light imaging and detection (LiDAR)
topographic data and 10Be geochronology of four offset alluvial fans, indicate a
northward increase in extension rate. The surface exposure ages of these fans range from
ca. 71 ka at Perry Aiken Creek and Indian Creek to ca. 94 ka and ca. 121 ka at Furnace
Creek and Wildhorse Creek, respectively. These ages, combined with the measured
vertical components of slip at each site, an assumed 60° fault dip, and a N65°E extension
direction, yield calculated late Pleistocene–Holocene horizontal extension rates of 0.1 ±
0.1, 0.3 ± 0.2, 0.7 +0.3/–0.1, and 0.5 +0.2/–0.1 mm/yr at Furnace Creek, Wildhorse
Creek, Perry Aiken Creek, and Indian Creek, from south to north, respectively.
Comparison of these rates with geodetic measurements of ~1 mm/yr of N65°E extension
across the northern Eastern California shear zone indicates that the Fish Lake Valley fault
accommodates approximately half of the current rate of regional extension. When
summed with published rates of extension for faults at the same latitude, the Fish Lake
Valley fault data indicate that long-term geologic deformation rates are commensurate
with short-term geodetic extension rates. The northward increase in Pleistocene extension
rates is opposite the northward decrease in dextral slip rate trend along the Fish Lake
19

Valley fault, likely reflecting a diffuse extensional transfer zone in northern Fish Lake
Valley that relays slip to the northeast across the Mina Deflection and northward into the
Walker Lane belt.

2.2 Introduction
The Eastern California shear zone–Walker Lane belt is an evolving fault system
east of the San Andreas fault that accommodates ~20% – 25% (9 – 10 mm/yr) of Pacific–
North America plate-boundary deformation (e.g., Dokka and Travis, 1990b; Humphreys
and Weldon, 1994; Hearn and Humphreys, 1998; Thatcher et al., 1999; Dixon et al.,
2000, 2003; McClusky et al., 2001; Miller et al., 2001; Bennett et al., 2003; Faulds et al.,
2005; Wesnousky, 2005a, 2005b; Frankel et al., 2007a). The Eastern California shear
zone extends northward for almost 500 km from the San Andreas fault through the
Mojave desert and along the eastern side of the Sierra Nevada. In the Mojave section of
the shear zone, fault motion is primarily right-lateral, with a subordinate component of
north-south shortening, and slip is localized along several major north-northwest–striking
faults (Dokka, 1983; Bartley et al., 1990; Dokka and Travis, 1990a, 1990b; Schermer et
al., 1996; Walker and Glazner, 1999; Glazner et al., 2002; Oskin et al., 2007a, 2007b,
2008). North of the active left-lateral Garlock fault, motion is accommodated on four
major fault systems: the Owens Valley, Panamint Valley–Saline Valley–Hunter
Mountain, Death Valley–Fish Lake Valley, and Stateline fault zones (Figure 2.1; e.g.,
Beanland and Clark, 1994; Lee et al., 2001, 2009a, 2009b; Oswald and Wesnousky,
2002; Kylander-Clark et al., 2005; Bacon and Pezzopane, 2007; Frankel et al., 2007a,
20

2007b, 2008a, 2008b; Guest et al., 2007; Kirby et al., 2008). In the northern part of the
Eastern California shear zone, between latitude 37°N and 38°N, dextral motion between
the stable Sierra Nevada block and North America is distributed from Long Valley
caldera in the west to the Silver Peak–Lone Mountain extensional complex in the east
(e.g., Burchfiel et al., 1987; Brogan et al., 1991; Berry, 1997; Reheis and Sawyer, 1997;
Hearn and Humphreys, 1998; Dixon et al., 2000; Oldow et al., 2001; Petronis, 2005;
Kirby et al., 2006; Frankel et al., 2007a, 2007b; Lee et al., 2009b). Multiple northeast-
striking, down-to-the-northwest normal faults transfer slip between the right-lateral
Owens Valley, Panamint Valley–Saline Valley–Hunter Mountain, and Death Valley–Fish
Lake Valley fault systems (Burchfi el et al., 1987; Applegate, 1995; Dixon et al., 1995;
Reheis and Dixon, 1996; Lee et al., 2001, 2009a; Oswald and Wesnousky, 2002; Walker
et al., 2005; Andrew and Walker, 2009). North of the Mina Deflection, strain is
accommodated by a series of right-lateral faults as part of the Walker Lane belt (e.g.,
Nielsen, 1965; Stewart, 1988; Oldow et al., 1989, 2001; Oldow, 2003; Wesnousky,
2005a, 2005b).
Although dextral shear accommodates most slip on the northwest-striking faults
in Fish Lake Valley, fault segments that strike more northerly exhibit a relatively large
extensional component of slip. Space-based geodetic studies demonstrate that the current
strain field is consistent with transtensional deformation and indicate an extension rate of
~1 mm/yr oriented normal (i.e., N65°E) to the predominant ~N25°W strike of the Eastern
California shear zone at this latitude (e.g., Savage et al., 2001; Bennett et al., 2003;
Wesnousky, 2005a). This extension rate in the northern Eastern California shear zone is
21

most likely distributed among the Sierra Nevada frontal fault, the faults of the Volcanic
Tablelands, the White Mountains fault, and the Fish Lake Valley fault system (Fig. 1).
The geologically determined component of the extension rates on the Sierra Nevada
frontal fault (Berry, 1997; Le et al., 2006) and the White Mountains fault (Kirby et al.,
2006) are both ~0.2–0.3 mm/yr, and the rate across the distributed normal faults of the
Volcanic Tablelands is ~0.3 mm/yr (Sheehan, 2007). Thus, the three main fault systems
to the west of the Fish Lake Valley fault collectively accommodate approximately half of
the current rate of extension within the northern part of the Eastern California shear zone.
In this paper, we investigate how much of the remaining extension is
accommodated by the Fish Lake Valley system. Specifically, herein we report new
observations from our analysis of high-resolution digital topographic airborne laser swath
mapping (light detection and ranging [LiDAR]) data, as well as terrestrial cosmogenic
nuclide (TCN) dating of faulted landforms along the Fish Lake Valley fault. Our results
provide new, geochronologically determined, late Pleistocene– Holocene extension rates
on this fault system that clarify how motion in the Eastern California shear zone is
accommodated and, ultimately, transferred northward to the Walker Lane belt. Moreover,
these results allow us to assess the degree to which short-term geodetic and longer-term
geologic rates are consistent, and the extent to which deformation is accommodated by
slip on geomorphically well-defined faults versus distributed, off-fault deformation.

22

Figure 2.1 Map of Quaternary faults in eastern California and western Nevada
showing the major right step in the Eastern California shear zone-Walker Lane
system across the Mina Deflection. Black and gray arrows show generalized fault-
parallel and fault-perpendicular components of geodetic velocity field (Bennett et
al., 2003; Wesnousky, 2005a). The outline of Figure 2.2 is indicated by a black
dashed line. Faults are from the U.S. Geological Survey (USGS) Quaternary fault
and fold database. AHF – Ash Hill fault, ALF – Airport Lake fault, BSF – Benton
Springs fault, CF – Coaldale fault, EF- Excelsior Mountains fault, EPF –
Emigrant Peak Fault, EVF – Eureka Valley fault, DSF – Deep Springs fault,
FLVF – Fish Lake Valley fault, GF – Garlock fault, HCF – Hilton Creek fault,
HMSVF – Hunter Mountain-Saline Valley fault, LMF – Lone Mountain fault,
MLF – Mono Lake fault, NDVF – northern Death Valley fault, OVF – Owens
Valley fault, PSF – Petrified Springs fault, PVF – Panamint Valley fault, QVF –
Queen Valley fault, RF – Rattlesnake Flat fault, RVF – Round Valley fault, SLF –
Silver Lake fault, SNF – Sierra Nevada frontal fault, TMF – Tin Mountain fault,
TPF – Towne Pass fault, WF- Warm Springs fault, WMF – White Mountains
fault.
23

2.3 Death Valley–Fish Lake Valley Fault Zone
The Fish Lake Valley fault, which forms the northern 80 km of the Death Valley–
Fish Lake Valley fault system, is marked by steep, east-facing fault scarps, ponded
drainages, and shutter ridges indicative of recent fault activity (Sawyer, 1990; Brogan et
al., 1991; Reheis, 1992; Reheis et al., 1993, 1995; Hooper et al., 2003; Frankel et al.,
2007a, 2007b, 2008b). The southern and central sections of the Fish Lake Valley fault
strike predominantly north-northwest, whereas the northern part of the fault is
characterized by numerous north- and northeast-striking strands that splay out into Fish
Lake Valley from the main north-northwest–trending, range-bounding fault (Figure 2.2;
Sawyer, 1991; Reheis and Sawyer, 1997).
Right-lateral motion on the Fish Lake Valley fault is thought to have begun ~10
m.y. ago (Reheis and Sawyer, 1997), and the strike-slip rate averaged over late
Pleistocene–Holocene time is 2.5–3 mm/yr (Frankel et al., 2007b). The extensional
component of oblique-normal-dextral motion, responsible for the opening of Fish Lake
Valley, most likely began ~5 m.y. ago, as suggested by the observation that the bounding
faults in the northern section of the valley cut across sedimentary rocks of the Miocene
Esmeralda basin (Reheis and Sawyer, 1997; Petronis et al., 2002, 2009; Petronis, 2005).
On the west side of the White Mountains, the right-lateral White Mountains fault
originated later, at ca. 3 Ma (Stockli et al., 2003). The late Pleistocene–Holocene White
Mountains fault oblique-slip rate is ~0.9 mm/yr, parallel to a net slip vector plunging
~20° toward N10°–20°W (Kirby et al., 2006).

24

Figure 2.2 Detailed map of the study area showing the Fish Lake Valley
fault in yellow. The locations of our study sites are labeled 1 through 4 from
south to north: 1 – Furnace Creek; 2 – Wildhorse Creek; 3 – Perry Aiken
Creek; 4 – Indian Creek. DSF – Deep Springs fault, EPF – Emigrant Peak
fault, FLVF – Fish Lake Valley fault, OVF – Owens Valley fault, QVF –
Queen Valley fault, WMF – White Mountains fault.
25

The focus areas of our study are normal fault scarps formed in four alluvial fans
along the Chiatovich Creek, Dyer, and Oasis sections of the fault, which have been
mapped in detail by a number of researchers (Brogan et al., 1991; Reheis, 1992; Reheis et
al., 1993, 1995). These four alluvial fans were deposited along the eastern White
Mountains piedmont at the mouths of (from south to north) Furnace Creek, Wildhorse
Creek, Perry Aiken Creek, and Indian Creek. We refer to each of our study sites relative
to the respective creek that formed them. At two of the sites, Furnace Creek and Indian
Creek, Frankel et al. (2007b) measured large (180–290 m) dextral offsets of alluvial
surfaces that they dated with cosmogenic
10
Be surface exposure geochronology at 94 ±
11 ka and 71 ± 8 ka, respectively. Their resulting right-lateral strike-slip rates at these
two locations are 3.1 ± 0.4 mm/yr at Furnace Creek and 2.5 ± 0.4 mm/yr at Indian Creek.
Multiple normal fault scarps are also present in both of these alluvial fans, as we discuss
in the following sections.
Our other two study sites, Wildhorse Creek and Perry Aiken Creek, are located
between the Furnace Creek and Indian Creek fans. Both the Wildhorse Creek and Perry
Aiken Creek sites have numerous normal fault scarps. The tallest single normal fault
scarp (minimum vertical component of displacement of 73.5 m) along the entire Death
Valley–Fish Lake Valley fault zone is found just north of Perry Aiken Creek (Reheis et
al., 1993; Reheis and Sawyer, 1997). Reheis et al. (1993) used tephrochronology to
suggest that alluvial fans at Wildhorse Creek and Perry Aiken Creek were deposited
during middle to late Pleistocene time.

26

2.4 Terrestrial Cosmogenic Nuclide Geochronology
We used terrestrial cosmogenic nuclide geochronology (TCN) to date the offset
alluvial fans along the Fish Lake Valley fault. TCN geochronology allows us to
determine the age of abandonment of an alluvial surface (e.g., Gosse and Phillips, 2001).
TCN geochronology measures the concentration of nuclides produced in a rock by the
interaction between cosmic rays and minerals at Earth’s surface (e.g., Lal, 1991; Gosse
and Phillips, 2001). In order to obtain an accurate age for abandonment of each sampled
geomorphic surface, several criteria must be satisfied: (1) the sampled boulder must be in
the same geometry as it was at the time of deposition; (2) the sampled boulder should not
have prior exposure history (inheritance); and (3) boulders with evidence of erosion
should not be sampled since they will provide an attenuated concentration of cosmogenic
isotopes and, hence, an anomalously young age (Gosse and Phillips, 2001).
The isotope of interest for this study is
10
Be, which is produced through spallation
and muon-induced reactions with Si and O in quartz. Beryllium-10 is well retained in
quartz, so we collected quartz-bearing samples from granitic boulders embedded in the
surface of the faulted alluvial fans. Fifteen samples were collected from the top 1–5 cm of
large granitic boulders (Table 2.1). These boulders came from the stable parts of fan
surfaces mapped by Reheis et al. (1993, 1995) as Qfm (alluvium of McAfee Creek) at
Wildhorse Creek and Qfi (alluvium of Indian Creek) at Perry Aiken Creek (Figure 2.3).
We carefully selected well-varnished boulders that lacked evidence of erosion (for
example, we did not sample ―sombrero-shaped‖ boulders). If, however, any erosion has
occurred, which we think is probably unlikely due to the arid climate in the study area,
27

the boulders would yield anomalously young ages, which would in turn make our
calculated slip rates too fast.
Quartz was purified by standard techniques, and Be was extracted using ion-
exchange chromatography, precipitated as BeOH, and converted to BeO at the Georgia
Institute of Technology cosmogenic nuclide geochronology laboratory (e.g., Kohl and
Nishiizumi, 1992; Bierman and Caffee, 2002). The
10
Be/
9
Be ratio for each sample was
measured at the Center for Accelerator Mass Spectrometry at Lawrence Livermore
National Laboratory, and model
10
Be ages were calculated using the CRONUS-Earth
10
Be-
26
Al exposure age calculator (version 2.1; http://hess.ess.washington.edu), and
constant
10
Be production rates (Lal, 1991; Stone, 2000; Balco et al., 2008) (Table 2.1). In
Table 2.1, we report the ages using a constant production rate, as well as time-varying
production rates calculated using four different models (Lal, 1991; Stone, 2000; Dunai,
2001; Desilets and Zreda, 2003; Lifton et al., 2005; Desilets et al., 2006). In reporting
ages and slip rates herein, we use the constant-production-rate model developed by Lal
(1991) and Stone (2000) to ensure consistency in our comparisons with the previously
determined ages of Frankel et al. (2007b), who used the same model for the Furnace
Creek and Indian Creek sites. Time-varying production rates could result in younger ages
by up to 10%, which would yield commensurately faster rates of extension.

28

Figure 2.3 Representative examples of sampled boulders from (A) the Qfi
deposit at Perry Aiken Creek, and (B) the Qfm deposit at Wildhorse Creek.
29

30

2.4.1 Perry Aiken Creek Fan Age
Nine TCN samples were analyzed from the Qfi alluvial-fan surface at Perry Aiken
Creek. The Qfi surface is characterized by subdued to moderately incised channels, well-
developed desert pavement, and a continuous, thick desert varnish on clasts. Clasts are
tightly packed and well sorted in a continuous pavement, and prominent solifluction
treads and risers are also present (Reheis and Sawyer, 1997). In addition, the Qfi deposit
is distinguished by a well-developed soil with a 5- to 10-cm-thick silty vesicular A
horizon, a weak argillic B horizon with thin clay films, and stage II to III carbonate
development (e.g., Reheis and Sawyer, 1997).
Our Qfi surface exposure ages exhibit a pronounced, single peak distribution with
a mean age and standard deviation of 71 ± 8 ka (Figure 2.4A). The ages range from 54 ±
5 ka to 79 ± 7 ka (Table 1). We take the tight clustering of ages as an indication that the
Qfi surface has remained relatively stable and that there is negligible inheritance. The age
we obtained for Qfi at Perry Aiken Creek is indistinguishable from the previously
determined 10Be age of 71 ± 8 ka for the Qfi deposit at Indian Creek by Frankel et al.
(2007b), and falls within the 50–130 ka age range estimated by Reheis and Sawyer
(1997) on the basis of soil development and surface morphology. The presence of an
extremely tight subcluster of six
10
Be ages centered at ca. 75 ka suggests that these ages
may most accurately reflect the age of abandonment of the Qfi surface at Perry Aiken
Creek. These six ages yield an age for the surface of 75.4 ± 2.2 ka. In this interpretation,
the three younger ages outside of the very tight 75 ka cluster would reflect either slight,
unrecognized erosion of the sampled tops of these boulders and/or minor exhumation of
31

Figure 2.4 Probability density functions of the
10
Be ages from surface boulders. (A)
Probability density function of the nine samples used to determine the age of Qfi at
Perry Aiken Creek. (B) Probability density function of the six samples used to
determine age of Qfm at Wildhorse Creek. The uncertainties are reported as the
mean and standard deviation.
32

these three clasts. Although we suspect that the slightly older 75.4 ± 2.2 ka age based on
the tight subcluster of six samples may more accurately reflect actual age of the surface,
in the following discussion, we use the 71 ± 8 ka age based on the entire suite of nine
samples for consistency with our other measurements and those of Frankel et al. (2007b).
We note, however, that if the tight ca. 75 ka cluster of six ages does represent the true age
of abandonment for the Qfi surface, then the slip rate we calculate from the 71 ± 8 ka age
range for all nine samples would yield values (both normal and strike-slip) that are ~5%
too fast.
2.4.2 Wildhorse Creek Fan Age
We analyzed six TCN samples collected from the Qfm alluvial-fan deposits at
Wildhorse Creek. The Qfm surface, referred to as ―alluvium of McAfee Creek‖ by
Reheis and Sawyer (1997), is characterized by subdued to moderately incised channels,
well-developed desert pavement, and a continuous, thick desert varnish on clasts. The
Qfm deposit exhibits a thick, silty vesicular A horizon, strong argillic B horizon, and
stage IV laminar carbonate development (e.g., Reheis and Sawyer, 1997). The pavement
is locally moderately well packed and well sorted, and abundant carbonate rubble is
present throughout (Reheis and Sawyer, 1997).
The six 10Be samples we dated from this surface range in age from 100 ± 9 ka to
140 ± 13 ka (Table 2.1), forming a relatively tight cluster at 121 ± 14 ka (Figure 2.4B).
As at Perry Aiken Creek, we take the clustered distribution of these ages as evidence that
the Qfm surface has remained relatively stable since the time of deposition and that
inheritance is minimal. The age we determined for the Qfm surface is significantly
33

younger than the 600?–760 ka age range proposed by Reheis and Sawyer (1997) on the
basis of soil development and surface morphology.
2.4.3 Furnace Creek and Indian Creek Fan Ages
The ages of the alluvial fans at Furnace Creek and Indian Creek were recently
determined by Frankel et al. (2007b) using cosmogenic
10
Be geochronology, and we
utilized their results to determine the extension rates at these two locations. At Furnace
Creek, Frankel et al. (2007b) reported an age for surface Qfio (modified from Qfi of
Reheis and Sawyer, 1997) of 94 ± 11 ka, whereas at Indian Creek, they determined the
age of surface Qfi y (modified from Qfi of Reheis and Sawyer, 1997) to be 71 ± 8 ka.
Both of these ages are in agreement with soil and fan morphology data reported
previously from those sites by Reheis and Sawyer (1997).

2.5. Geomorphic Analysis of Normal Fault Scarps
The analysis of LiDAR digital topographic data is an integral component of our
study. The LiDAR data were collected in the fall of 2005 by the National Center for
Airborne Laser Mapping (NCALM) using an Optech Inc. model ALTM 2033 laser
mapping system. The laser was installed on a Cessna 337 twin-engine airplane, which
flew over the fault trace at an average elevation of 600 m above ground level and an
average speed of 60 m/s. The pulse rate frequency of the Optech ALTM 2033 was set at
33 kHz, and it recorded the first and last returns of each pulse, plus the relative intensity
of each return. The average shot density for the LiDAR data was ~3 points/m2. The
aircraft was equipped with a dual-frequency global positioning system (GPS) receiver
34

and a real-time display of the flight path and area coverage. High-resolution digital
elevation models (DEMs) with 5–10 cm vertical accuracy and 1 m horizontal resolution
were produced using a kriging algorithm in SURFER software (version 8.04; Carter et
al., 2007; Sartori, 2005).
ArcGIS (version 9.2) was used to produce hill-shaded relief and topographic maps
to aid in the identification and mapping of all normal fault scarps at each site. We
analyzed a total of 25 profiles perpendicular to the strike of each set of scarps at the four
study sites. The vertical displacement components for each set of faults were measured
by multiple topographic profiles, and the means of these measurements were calculated
(Figure 2.5; Figure A1 and Table A1). The total vertical component of displacement for
each site was determined by summation of the mean values. The horizontal component of
each displacement was subsequently calculated using simple trigonometric relationships
by assuming a 60° dip of the fault plane for each scarp (e.g., Kirby et al., 2006; Le et al.,
2006, 2009a). Uncertainties associated with measurements of the vertical components of
each displacement include surface roughness (~20 cm) and the vertical accuracy (~10
cm) of the LiDAR data. Combined, these two uncertainties are <5% of the total mean
vertical component of displacement at each site, and thus we report a conservative
displacement error of 5%. This 5% error is also carried over to the extensional
component of displacement. We report the horizontal (extensional) component of
displacement across the fault zone at each of the four sites, rather than the total vertical
separation, due to the presence of multiple scarps associated with antithetic faults.
Antithetic faults would lead to a reduction in the net vertical displacement across the fault
35

Figure 2.5 Selected topographic profiles across alluvial-fan surfaces and
calculated vertical components of displacement from the four study sies:
(A) Furnace Creek; (B) Wildhorse Creek; (C) Perry Aiken Creek; and
(D) Indian Creek. See Figures 2.7-2.10 for locations of the profiles. The
gray and black lines on profile P-P’ in Figure 2.5A represent the vertical
component of displacement between two laterally juxtaposed features.
36

zone. Therefore, we feel that the total extension represents a more robust measure of the
net fault slip. At each site, we determined an extension direction that is normal to the
average strike of the faults. Due to the presence of multiple sets of faults with different
orientations at Furnace Creek, Wildhorse Creek, and Indian Creek, we resolved the
cumulative extension at these three sites as the sum of the extension vectors
for each fault set (Figure 2.6).
One concern in this type of analysis is the oblique nature of slip on the Fish Lake
Valley fault (Figures 2.7-2.10). In the absence of direct field evidence for the rake of
oblique slip (e.g., slickensides), we analyzed the difference between horizontal extension
and right-lateral slip along the main right-lateral fault strand at each of our four study
sites. Specifically, at each site, we used restorations of total strike-slip motion to define
the pre-offset geometry of the dated alluvial-fan surfaces. Any scarps that exhibit a
vertical component of slip on the restored surfaces must be caused by true dip-slip
motion, and we used measurements of those scarp heights in our analysis of extension.
We used the strike-slip restorations of Frankel et al. (2007b) for this analysis at the
Furnace Creek and Indian Creek sites. As discussed later, we provide a new strike-slip
restoration and strike-slip rate at the Perry Aiken site. In marked contrast to the other
three study sites, we could not determine a unique strike-slip restoration at the Wildhorse
Creek site, so we used the strike-slip rate of the fault determined by Frankel et al. (2007b)
and the age of the offset alluvial surface to provide an approximate restoration. Given the
overall similarity of the three well-constrained strike-slip rates that are now available
37

Figure 2.6 Vector resolutions for horizontal extension at (A) Furnace Creek; (B1)
Wildhorse Creek- profiles N-N’ and O-O’; (B2) Wildhorse Creek- profiles NN-NN’
and OO-OO’; (C) Perry Aiken Creek; and (D) Indian Creek. Error circles
represent 5% of total amount of displacement. Note that for (A) Furnace Creek and
(D) Indian Creek, we resolve the vector sums for two different sets of faults in order
to calculate total horizontal extension.
38

Figure 2.7 Hill-shaded, LiDAR-derived digital elevation model (DEM) of the
Furnace Creek site showing the topographic profiles analyzed. The number by each
fault scarp represents the scarps that we included in our analysis, and it
corresponds to the fault number in Table 2.1. The mapped Quaternary deposits
were modified from Reheis et al. (1993). See Table A1 in Appendix A for the
detailed measurements of scarps heights. Solid lines are fault scarps (used in
analysis), dashed lines are fault scarps visible on shaded relief maps but not
detectible on topographic profiles (not used in analysis), arrows show sense of
motion on strike-slip faults, tick marks are on the hanging wall of normal faults.
39

Figure 2.8 Hill-shaded, LiDAR-derived digital elevation model (DEM) of the
Wildhorse Creek site showing the topographic profiles analyzed. The white dots
indicate the locations of the dated samples. The number by each fault scarp
represents the scarps that we included in our analysis, and it corresponds to the
fault number in Table 2.1. The mapped Quaternary deposits were modified from
Reheis et al. (1993). See Table A1 in Appendix A for the detailed measurements of
scarps heights. Solid lines are fault scarps (used in analysis), dashed lines are fault
scarps visible on shaded relief maps but not detectible on topographic profiles (not
used in analysis), arrows show sense of motion on strike-slip faults, tick marks are
on the hanging wall of normal faults, and dashed lines with question marks denote
inferred fault scarps and sense of motion.
40

Figure 2.9 Hill-shaded, LiDAR-derived digital elevation model (DEM) of the Perry
Aiken Creek site showing the topographic profiles analyzed. The white dots indicate
the locations of the dated samples. The number by each fault scarp represents the
scarps that we included in our analysis, and it corresponds to the fault number in
Table 2.1. The mapped Quaternary deposits were modified from Reheis et al.
(1993). See Table A1 in Appendix A for the detailed measurements of scarps
heights. Solid lines are fault scarps (used in analysis), dashed lines are fault scarps
visible on shaded relief maps but not detectible on topographic profiles (not used in
analysis), arrows show sense of motion on strike-slip faults, tick marks are on the
hanging wall of normal faults.

41

Figure 2.10 Hill-shaded, LiDAR-derived digital elevation model (DEM) of the
Indian Creek site showing the topographic profiles analyzed. The white dots
indicate the locations of the dated samples. The number by each fault scarp
represents the scarps that we included in our analysis, and it corresponds to the
fault number in Table 2.1. The mapped Quaternary deposits were modified from
Reheis et al. (1993). See Table A1 in Appendix A for the detailed measurements of
scarps heights. Solid lines are fault scarps (used in analysis), dashed lines are fault
scarps visible on shaded relief maps but not detectible on topographic profiles (not
used in analysis), arrows show sense of motion on strike-slip faults, tick marks are
on the hanging wall of normal faults.
42

along the fault (Furnace Creek and Indian Creek from Frankel et al. [2007b]; Perry Aiken
Creek as documented herein), we think that this restoration is likely to be approximately
correct.
2.5.1 Furnace Creek
Two fault sets are prominent at the Furnace Creek site: north-northwest–trending
faults of the main, predominantly right-lateral strand of the Fish Lake Valley fault, and a
northeast-trending set of distributed normal faults to the east. In order to account for the
difference in strike between the two sets of faults at this site, we resolved the extension
measured by the profiles from the two fault sets as a vector sum oriented toward N83°E
(Figure 2.7). Transects PP′-P1P1′ and QQ′-Q1Q1′, and R-R′ through W-W′ are
superimposed in order to capture the vertical component of displacement across two
scarps that juxtapose the right-laterally offset alluvial fan (Figures 2.5A and 2.7).
Inasmuch as right-lateral offset of the alluvial fan at this location will result in apparently
smaller scarp heights due to juxtaposition of laterally variable topography, these profiles
provide us with the minimum vertical displacement. In order to determine a more
accurate measurement of potential dip-slip motion on the mountain-front strand, we used
the strike-slip restoration of Frankel et al. (2007b). These authors showed that restoration
of 290 ± 20 m of right-lateral slip realigns the cone-shaped geometry of the Qfi fan as
well as a major incised drainage (their Fig. 2). Our measurement of residual scarp heights
on the Frankel et al. (2007b) restoration indicates a vertical component of displacement
of 8 ± 1 m. This small amount of oblique-normal displacement indicates that the main
mountain-front fault strand at Furnace Creek is a near-pure right-lateral strike-slip fault
43

(strike-slip/normal: 290/8), with a slip direction oriented N48°W, plunging at 3° toward
the northwest.
In marked contrast to the predominantly right-lateral oblique-slip mountain-front
strand, the scarps we mapped to the east do not exhibit any apparent strike slip,
suggesting that they are nearly pure dip-slip faults. We used profiles X-X′ and Y-Y′ to
capture the horizontal component of extensional displacement across these northeast-
oriented scarps. By combining the extension we measured across these faults with that on
the main, mountain-front fault strand, we get a cumulative mean horizontal extension
across all faults at Furnace Creek of 13.0 ± 0.7 m toward N83°E (Figure 2.6A).
2.5.2 Wildhorse Creek
Unlike the other three study sites, we could not determine a well-defined strike-
slip offset along the mountain-front strand (Figure 2.8) at Wildhorse Creek. We therefore
used the well-constrained 3.1 ± 0.4 mm/yr of Frankel et al. (2007b) from the nearby
Furnace Creek site (5 km south) and the 121 ± 14 ka age of the Wildhorse Creek Qfm
surface to estimate total strike-slip offset of the Qfm surface of ~350 m. This restoration
matches a shutter ridge to the east with the Qfm deposits from the main alluvial fan
formed out of Wildhorse Creek (Figure 2.11). This admittedly crude strike-slip
restoration indicates that there is some oblique displacement along the main fault strand,
which is best observed on the restored surface north of the creek. We estimate the height
of the scarp on the restored fan surface north of Wildhorse Creek to be less than 15 m.
We note that this observation is relatively insensitive to the details of our approximate
strike-slip restorations, as changing the restoration by 40 m does not result in a significant
44

change in scarp height. This suggests that motion along the main mountain- front fault
strand at Wildhorse Creek is predominantly strike slip.
The two profiles (N-N′ and O-O′) we analyzed north of Wildhorse Creek were
oriented to most effectively capture all of the identifiable fault scarps (Figures 2.5B and
2.8). Profile N-N′ measured four smaller scarps striking approximately N5°W, whereas
profile O-O′ measured the scarp along the main mountain-front fault strand, which strikes
N40°W. Although some of the scarps are antithetic, which would lead to a reduction in
the net vertical displacement across the fault zone, it does not affect our calculations in
terms of horizontal displacement. The cumulative mean horizontal component of
extensional displacement at Wildhorse Creek is 52.3 ± 2.6 m toward N53°E (Figure
2.5B).
The two profiles (NN-NN′ and OO-OO′) that we measured across the normal fault
scarps south of Wildhorse Creek provide additional information about the distribution of
slip on this section of the Fish Lake Valley fault. Specifically, although we could not
effectively measure the amount of extension across the main, mountain-front strand south
of Wildhorse Creek because of the presence of a prominent pressure ridge along this part
of the fault system, we were able to measure the amount of extension accommodated to
the west of the mountain-front strand along several north-northwest–trending normal
faults that add slip to the mountain-front system from the southwest. Specifically, profiles
NN-NN′ and OO-OO′ indicate that these faults have accommodated a total of 19.9 ± 1.0
m of extension oriented toward N77°E since abandonment of the Qfm surface (Figure
2.6B).
45

As discussed later, northward addition of this extra component of extension from
distributed extension within the White Mountains partially accounts for the northward
increase in extension rates that we observe along the Fish Lake Valley fault system.
2.5.3 Perry Aiken Creek
The fault zone at Perry Aiken Creek exhibits a complex pattern of sub-parallel,
anastomosing fault strands (Figure 2.9). This section of the fault includes one of the
tallest single fault scarps in Fish Lake Valley, located just north of the mouth of Perry
Aiken Creek. This 73.5-m-tall fault scarp provides clear evidence for significant normal
displacement. However, the fault strand also exhibits evidence for large right-lateral
strike-slip displacement. Specifically, backslipping the main, mountain-front fault strand
by 250 m restores the right-laterally offset Qfi terrace riser along the margins of Perry
Aiken Creek (Figure 2.11). Combining the 250 m offset with the 71 ± 8 ka age for the
nine
10
Be samples from the Qfi surface yields a strike-slip rate of ~3.2–4.0 mm/yr,
similar to, but slightly faster than, the 3.1 ± 0.4 mm/yr rate calculated by Frankel et al.
(2007b) from the Furnace Creek site to the south. Alternatively, if, as we suspect, the
75.4 ± 2.2 ka age for the very tight cluster of six ages from the Perry Aiken fan surface
more accurately reflects the age of abandonment of the Qfi surface, then the strike-slip
rate would be slightly slower at ~3.2–3.4 mm/yr. We also note that on the restored image
(Figures 2.11C-2.11D; Figure A2) there remains a pronounced right deflection of the
Perry Aiken Creek canyon ~300 m west of (i.e., upstream from) the main strike-slip fault
strand. It is possible that this represents an additional strike-slip strand, which would
increase the strike-slip rate at this site. However, the westernmost main fault strand that
46

extends southward to near this right deflection does not appear to cross the canyon,
suggesting that the deflection may be purely of fluvial origin, perhaps at a bend in the
stream localized at one of the minor normal fault scarps that extend through this area.
The presence of a significant component of strike slip at this site raises the
possibility that the very tall scarp just north of Perry Aiken Creek is due partially to
strike-slip offset of laterally varying topography. However, measurements of four
topographic profiles across all strands of the fault system, including across the tallest part
of the scarp north of Perry Aiken Creek, yield strikingly similar amounts of total vertical
separation on the Qfi surface of 85.1 ± 4.3 m (Figures 2.5C and 2.9). The similarity of
these measurements along different profiles suggests that this is a robust observation of
the total vertical component of oblique slip at the Perry Aiken Creek site. Moreover,
along profiles L-L′ and M-M′, the Qfi surface is buried beneath the gently north-sloping,
northern shoulder of a younger fan east of the fault zone, indicating that the vertical
measurements on those profiles are minima. The vertical component of total
displacement is in agreement with previous measurements by Reheis and Sawyer (1997),
who suggested 85.5 m of vertical separation on the Qfi surface. Based on our 85.1 ± 4.3
m measurement of total vertical separation, the cumulative mean horizontal extensional
component of displacement at Perry Aiken Creek is 49.1 ± 2.5 m toward N68°E (Figures
2.6C). A comparison of the extensional and strike-slip components of slip indicates that
the Fish Lake Valley fault at Perry Aiken Creek is primarily a right-lateral strike-slip
fault, with a strike-slip to dip-slip ratio of ~5:1 (i.e., 250 m:49 m).

47

2.5.4 Indian Creek
At the Indian Creek site, we analyzed nine topographic profiles across two
different sets of fault scarps (Figures 2.5D and 2.10). Profile A-A′ extends across the two
normal fault scarps, one facing east and one facing west, to the west of the range-front
dextral fault strand. We used profile B-B′ to capture the horizontal extensional
displacement across the main right-lateral strand of the fault. This profile provides us
with a minimum vertical displacement, as right-lateral offset of the alluvial fan at this
location will result in apparently smaller scarp heights due to juxtaposition of laterally
variable topography. As at Furnace Creek, we used the strike-slip restoration of Frankel
et al. (2007b) to determine a more accurate measurement of potential dip-slip motion on
the mountain-front strand. Frankel et al. (2007b) showed that restoration of 178 ± 20 m of
right-lateral slip realigns numerous incised drainages, as well as the overall limits of the
Qfi fan (their Fig. 3). Our measurement of residual scarp heights on the Frankel et al.
(2007b) restoration indicates a vertical component of displacement of 23 ± 1 m. By
combining the horizontal and vertical components of slip, we find a total oblique
displacement of the Qfi surface of 179 ± 20 m, with a slip direction plunging 7° toward
N30°W. Profiles C-C′ through I-I′ were used to measure the displacement across a set of
distributed, north-northeast–trending normal faults to the east. In order to account for the
difference in strike between the main strand and the eastern fault set, we resolved the
extension measured by the profiles from the two fault sets as a vector sum. The
cumulative mean horizontal extensional displacement at Indian Creek is 43.7 ± 2.1 m
toward S88°E (Figures 2.6D). The cumulative vertical displacement across all fault
48

strands at this site (75.4 ± 3.8 m) is almost twice as large as the previously reported
preferred vertical component of displacement of 40 m by Reheis and Sawyer (1997).

49

Figure 2.11 Hill-shaded geologic (A and C), and topographic (B and D) maps of
Wildhorse Creek (top) and Perry Aiken Creek (bottom) alluvial fans derived from
light detection and ranging (LiDAR) data. Although no unequivocal right-lateral
restoration is apparent, we retrodeformed the Wildhorse Creek fan by ~360 m by
combining the strike-slip rate from the nearby Furnace Creek site (Frankel et al.,
2007b) and the age of the Wildhorse Creek fan. This yielded an acceptable
restoration of the main channel of Wildhorse Creek, as well as for an incised
drainage ~400 m to the north. At Perry Aiken Creek, restoration of 250 m of right-
lateral strike slip restored the channel margins of the incised Perry Aiken Creek,
yielding a strike-slip rate of ~3.0-3.5 mm/yr, similar to the 3.1 ± 0.4 mm/yr rate
determined by Frankel et al. (2007b) at the Furnace Creek site.
50

2.6 Summary of Rate Data along the Fish Lake Valley Fault
We calculated extension rates at each of our four study sites by combining
vertical components of displacement, fan surface ages, and an assumed 60° fault dip.
Specifically, our extension rates were computed by combining probability density
functions of the measured displacements and TCN ages. These extension rates were first
calculated in their original extension direction, and then resolved to an extension
direction of N65°E to facilitate comparison with geodetic measurements of extension
rates (Table 2.2). We used a Gaussian uncertainty model (e.g., Bird, 2007; Kozaci et al.,
2009; McGill et al., 2009; Zechar and Frankel, 2009), and the uncertainties in the
extension rates are reported at the 2σ confidence interval. The resulting extension rates
from south to north are: Furnace Creek = 0.2 ± 0.1 mm/yr toward N83°E, Wildhorse
Creek = 0.4 ± 0.2 mm/yr toward N53°E, Perry Aiken Creek = 0.7 +0.3/–0.1 mm/yr
toward N68°E, and Indian Creek = 0.6 +0.2/–0.1 mm/yr toward S88°E.
The
10
Be dates from all four of our sites should be considered maximum ages for
calculating the extension rates because the normal fault scarps must have developed after
the deposition and abandonment of the Qfi and Qfm alluvial-fan deposits. However,
inasmuch as extension has been active at similar rates along the Fish Lake Valley fault
system for at least 760 k.y. (Reheis and Sawyer, 1997), any time lag between fan
abandonment and initial extensional deformation of the fan surface is likely to have been
brief compared with the late Pleistocene ages of the measured fans. Thus, this source of
potential error will have a negligible effect on our calculated extension rates. However,
although we are confident that we have captured all of the main fault strands that exhibit
51

52

a normal component of slip, some distributed deformation that does not manifest itself as
recognizable fault scarps could be present. Furthermore, in our analysis, we do not
include minor fault strands that are visible on the LiDAR data, but which exhibit scarp
heights of <0.5 m, which we consider to be close to the resolution limit of this technique.
In addition, assuming a steeper fault dip angle, for example, 75°, would lower each of the
extension rates by ~50%. The oblique, predominantly strike-slip motion along the Fish
Lake Valley fault might at first suggest that the dip of the faults may indeed be somewhat
steeper than 60°. As noted already, however, the fault system is largely strain partitioned
into strike-slip and normal faults, lending confidence to our assumption of a 60° dip angle
for the extensional faults. If steeper faults do exist, they would most likely be the
mountain-front strands at Wildhorse Creek and Perry Aiken Creek, where they exhibit
oblique motion. Thus, the extension rates we calculate for these sites may be maxima.
We emphasize, however, that we do not have any direct measurements of the dip of these
faults.

2.7 Discussion
The new rate data described here allow us to place quantitative constraints on the
style and location of northward strain transfer through the Mina Deflection from faults of
the Eastern California shear zone to structures in the Walker Lane belt. The extension
rates we obtained on the Fish Lake Valley fault increase northward from 0.2 ± 0.1 mm/yr
at Furnace Creek, to 0.4 ± 0.2 and Wildhorse Creek, and to 0.7 + 0.3/-0.1 mm/yr and 0.6
+ 0.2/-0.1 mm/yr at the Perry Aiken Creek and Indian Creek sites, respectively. These
53

extension rates are similar to those estimated by Reheis and Sawyer (1997), who reported
a preferred late Pleistocene vertical component of oblique slip at Furnace Creek of 0.3
mm/yr and 0.8 mm/yr at Indian Creek, on the basis of tephrochronology. If we assume a
60° dip for the fault plane, their preferred extension rates at Furnace Creek and Indian
Creek would be 0.2 mm/yr and 0.5 mm/yr, respectively. No preferred vertical component
of total slip rate was reported by Reheis and Sawyer (1997) for Wildhorse Creek and
Perry Aiken Creek.
At our Wildhorse Creek site, we were able to quantify the amount of extension
that has been added to the Fish Lake Valley fault system between that site and the
Furnace Creek site to the south. Specifically, we used two profiles (NN-NN′ and OO-
OO′) just south of Wildhorse Creek that capture normal fault scarps that provide
additional extension to the fault system. When resolved to N65°E, the extension rate on
the fault set west of the main strand is 0.2 ± 0.1 mm/yr. Profiles N-N′ and O-O′, located
to the north of Wildhorse Creek, demonstrate that the cumulative extension rate oriented
toward N65°E at the northern part of the Wildhorse Creek site is 0.3 ± 0.2 mm/yr. Thus,
the addition of the extension accommodated by the western fault set increases the overall
extension rate at Wildhorse Creek by 0.1 ± 0.1 mm/yr. This is consistent with our
observation that the extension rate oriented toward the geodetically defined current
extension direction of N65°E increases northward from 0.1 ± 0.1 mm/yr at Furnace Creek
to 0.3 ± 0.2 mm/yr at Wildhorse Creek, and it suggests that significant extension may be
accommodated by distributed normal faulting within the White Mountains to the
southwest of the Wildhorse Creek site.
54

It is possible that the northward increase in extension rates that we measured
along the Fish Lake Valley fault is a manifestation of a temporally variable slip rate,
rather than along-strike variations in slip, inasmuch as we compared offset alluvial fans
that span a wide range of ages between 71 ± 8 ka and 121 ± 14 ka. If this change is due to
temporal variation in slip rate, then the extension rate must have accelerated since ca. 94
ka (the age of Furnace Creek alluvial fan) by a factor of 2–3 times to account for the
more rapid extension observed in the younger Perry Aiken Creek and Indian Creek fans.
Moreover, the overall consistency between our late Pleistocene extension rates (averaged
over 71 k.y. to 121 k.y., depending on the site) and the longer-term rates of Reheis and
Sawyer (1997; averaged over 760 k.y.) suggests that the extension rate may be relatively
constant over a wide range of time scales. Thus, although we cannot rule out a temporal
change in extension rates, we think that a more likely explanation lies in the overall
geometry of the fault system and the manner in which slip is transferred northward from
the Eastern California shear zone into the Walker Lane belt across the Mina Deflection.
2.7.1 Geodetic versus Geologic Rates of Extension
In order to compare short-term geodetic and longer-term geologic extension rates
at the latitude of Fish Lake Valley, we resolved the geologic extension-rate vectors from
our four study sites toward the extension direction of N65°E defined by the geodetically
constrained models of Bennett et al. (2003) and Wesnousky (2005a). The resulting
N65°E extension rates at our four sites are 0.1 ± 0.1 mm/yr at Furnace Creek, 0.3 ± 0.2
mm/yr at Wildhorse Creek, 0.7 +0.3/–0.1 mm/yr at Perry Aiken Creek, and 0.5 +0.2/–0.1
at Indian Creek (Table 2.2).
55

As noted already, at the latitude of Fish Lake Valley, over geologic time scales,
approximately half of the current 1.0 mm/yr (Wesnousky, 2005b) extension rate defined
by short-term geodetic data is accommodated by faults to the west, including the White
Mountains fault (Kirby et al., 2006), distributed normal faulting in the Volcanic
Tablelands (Kirby et al., 2006; Greene et al., 2007; Sheehan, 2007; data of Greene and
Kirby in Frankel et al., 2008a), and the Sierra Nevada frontal fault system (Le et al.,
2006), including the Round Valley and Hilton Creek faults north of Owens Valley
(Figure 2.12; Berry, 1997). The oblique-normal-dextral White Mountains fault exhibits a
late
Pleistocene extension rate at the latitude of our Furnace Creek site of ~0.2 mm/yr
(Kirby et al., 2006), whereas at approximately the same latitude, there is clear evidence
for distributed normal faulting across the Volcanic Tablelands (e.g., Sheehan, 2007;
Pinter and Keller, 1995). Sheehan (2007) reported an extension rate across the Volcanic
Tablelands of ~0.3 mm/yr. Further west at the same latitude, Berry (1997) reported a 0.5–
0.6 mm/yr late Pleistocene vertical component of slip on the Round Valley fault. This is
equivalent to an extension rate on a 60° dipping fault of ~0.3 mm/yr.
Combining all of these extension rates with our rates from the Fish Lake Valley
fault, the N65°E component of extension for all of the major fault systems in the
northernmost Eastern California shear zone, from the Sierra Nevada fault to the west and
the Fish Lake Valley fault to the east, is approximately equal to the geodetically
determined extension rate at the latitude of central/northern Fish Lake Valley. This
comparison suggests that the rate of extension at the latitude of northern Fish Lake Valley
56

Figure 2.12 Rates of horizontal extension on faults in the Eastern California shear
zone between 37°N and 38°N latitude. The rates on the Round Valley fault (RVF)
and Hilton Creek (HCF) are from Berry (1997), the rate on the Volcanic Tablelands
is from Sheehan (2007), the rate on the White Mountains fault (WMF) is from Kirby
et al. (2006), and the rates on the Fish Lake Valley fault (FLVF) are from this study.
In some of these publications, the authors report only the vertical component of slip;
therefore, we resolved the extension rates by assuming a 60° fault dip on the faults.
DSF – Deep Springs fault, EPF – Emigrant Peak fault, FLVF – Fish Lake Valley
fault, HCF – Hilton Creek fault, OVF – Owens Valley fault, QVF – Queen Valley
fault, RVF – Round Valley fault.
57

may have remained relatively constant over the past 104–105 yr, although it is also
possible that temporal variations in slip rate have occurred over shorter time scales on the
various faults that accommodate extension across the region. Additional slip rate
calculations on all of these faults at a wider span of time scales are necessary to test
whether such temporal variations in rate have occurred.
2.7.2 Strain Transfer at the Eastern California Shear Zone – Walker Lane
Transition
The Fish Lake Valley fault terminates just north of Indian Creek, and slip from
this fault, as well as the White Mountains–Queen Valley and Tablelands fault systems to
the west, is transferred northeastward across the Mina Deflection onto oblique-normal
right-lateral faults of the Walker Lane belt. Thus, the Mina Deflection can be thought of
as a major (~80-km-wide), east-trending right step in a dominantly right-lateral, north-
northeast-trending fault system (Stewart, 1988; Dixon et al., 1995; Reheis and Dixon,
1996; Oldow et al., 1989, 1994, 2001, 2009; Lee et al., 2001, 2006, 2009a, 2009b;
Petronis et al., 2002, 2009; Oldow, 2003; Stockli et al., 2003; Wesnousky, 2005a, 2005b;
Kirby et al., 2006; Frankel et al., 2007b; Sheehan, 2007). Within the Mina Deflection,
deformation is accommodated by east-trending left-lateral faults and clockwise block
rotations (Stewart, 1985; Cashman and Fontaine, 2000; Faulds et al., 2005; Wesnousky,
2005a).
As documented by Frankel et al. (2007b) and the Perry Aiken strike-slip rate we
present herein, the strike-slip rate decreases northward along the Fish Lake Valley fault,
from 3 to 3.5 mm/yr at Furnace Creek and Perry Aiken Creek, to 2.5 mm/yr at our
58

northernmost study site at Indian Creek. The northward decrease in right-lateral slip rate
is even more pronounced in the northernmost part of Fish Lake Valley, where the surface
expression of the fault zone ends abruptly ~10 km north of Indian Creek. The observation
that extension rates increase northward along the Fish Lake Valley fault, whereas dextral
rates decrease, has important implications for the distribution of strain along this section
of the Pacific–North America plate boundary, and more generally for mechanisms of slip
transfer along evolving, structurally complex fault systems (Figure 2.12).
In general, both the northward increase in extension rate that we document and
the northward decrease in dextral slip rate documented by Frankel et al. (2007b) reflect
transfer of slip off the predominantly right-lateral Fish Lake Valley fault and onto north-
and northeast-trending normal faults as part of a distributed zone of slip transfer located
in the ~40-km-long by 30-kmwide, triangular area east of the Fish Lake Valley fault
between the Emigrant Peak fault and the east-trending left-lateral faults of the Mina
Deflection (Figure 2.2). For example, the north-northeast-trending normal faults that cut
the fan to the east of the main range-front fault strands at the Furnace Creek site appear to
―pull‖ slip off the Fish Lake Valley fault system and transfer it northeastward onto the
Emigrant Peak fault system (Figure 2.6). Similarly, the north-northeast-trending normal
faults at Indian Creek serve to transfer slip off the Fish Lake Valley fault and into the
zone of distributed normal faulting in this corner of Fish Lake Valley, leaving only 2.5
mm/yr of right-lateral strike-slip motion on the Fish Lake Valley fault at this site (Figure
59

2.9; Frankel et al., 2007b). This diffuse normal faulting along with normal displacements
on the prominent Emigrant Peak fault system account for the development of the deep
basin that defines the northeast-trending part of northern Fish Lake Valley (including the
dry ―Fish Lake‖ proper; Figure 2.12). The most pronounced decrease in right-lateral
strike-slip rate along the Fish Lake Valley fault occurs just north of the Indian Creek site,
where the geomorphic expression of the fault system dies out completely within a zone of
extensive recent lava flows in the Volcanic Hills (Figure 2.12). Between Indian Creek
and the northwestern limit of faulting observable on the LiDAR data within the southern
part of the Volcanic Hills, the Fish Lake Valley fault system splays northward into an
increasingly distributed set of numerous small-scale normal faults. Thus, between the
north end of the geomorphically well-defined Fish Lake Valley fault at Indian Creek, and
the left-lateral faults of the Mina Deflection to the north, it appears that distributed
normal faulting may accommodate as much as 2.5 mm/yr of dextral motion. The
coincidence of this zone of apparent distributed normal faulting and the extensive
volcanism in the Volcanic Hills suggests that the volcanism may be localized by this slip
transfer zone. The young volcanism in this area may also serve to obscure geomorphic
evidence for recent normal faulting.
60

Ultimately, much of this motion must be accommodated along the east-west-
trending left-lateral faults of the Mina Deflection (Figure 2.1; e.g., the Coaldale,
Excelsior Mountains, and Rattlesnake Flat faults) (Stewart, 1985; Wesnousky, 2005a;
Lee et al., 2009a). However, the manner in which this slip transfers northward onto the
left-lateral faults remains unclear because there are no geomorphically well-expressed
faults in the 10-km-wide zone between the northern end of the Fish Lake Valley fault and
the Coaldale fault (Figure 2.12). If, as we suspect, this slip is transferred northward into
the Mina Deflection along a diffuse set of highly distributed normal faults beneath the
Volcanic Hills, then this would imply that clockwise rotations and/or left-lateral slip rates
on the Mina Deflection faults would increase eastward.
One possibility that we consider is that the northeast-trending normal faults that
characterize the northern part of Fish Lake Valley represent an early stage in the
evolution of faults similar to the east-trending left-lateral faults of the Mina Deflection. In
such a scenario, these faults would develop as northeast-trending normal faults that act to
transfer strain across the major right step of the Mina Deflection. As noted in
Wesnousky’s (2005a) earlier model for the structural evolution of the Mina Deflection, in
response to ongoing right-lateral shear, these northeast-trending normal faults would
gradually rotate clockwise into a more east-west orientation, switching to left-lateral
strike-slip motion as a result of this reorientation. However, both the well-established
nature of the north-east-trending basin along the north side of the Silver Peak Range and
61

long-term activity of the north- to northeast-trending Emigrant Peak fault system
(Petronis et al., 2002, 2009; Petronis, 2005) argue that these are well-established, long-
lived features that do not appear to be actively rotating. In either case, slip transfer across
the northern end of Fish Lake Valley into and across the Mina Deflection appears to
involve a large component of distributed normal faulting, as well as left-lateral strike-slip
faulting, perhaps quite distributed at the northwest corner of the valley, and clockwise
rotations (Figure 2.13).

62

Figure 2.13 Fault model showing the
development of northeast-striking normal
faults transferring strain in a right stepover
between two northwest-striking zones of right-
lateral shear. Clockwise rotation of the normal
faults is necessary to achieve the highest
efficiency in slip transfer. Along the Fish Lake
Valley fault (FLVF), the right-lateral slip rate
decreases northward near the Mina
Deflection, where there is an increase in the
extension rate of the fault zone. These
observations indicate the presence of a zone of
distributed strain transfer between the
northern Eastern California shear zone and
Walker Lane belt in the northwestern part of
Fish Lake Valley. BSF – Benton Springs fault;
CF – Coaldate fault; EF – Excelsior
Mountains fault; FLVF – Fish Lake Valley
fault; RF – Rattlesnake Flat fault; SP – Silver
Peak.
63

2.8 Conclusions
New LiDAR topographic data and cosmogenic
10
Be geochronology of offset
alluvial-fan deposits on the dextral-oblique Fish Lake Valley fault yield well-determined
late Pleistocene-Holocene extension rates on this major oblique-normal-dextral fault
system. The surface exposure ages of four sites, Furnace Creek, Wildhorse Creek, Perry
Aiken Creek, and Indian Creek (from south to north), range from 71 ± 8 ka to 121 ± 14
ka, and the mean horizontal extensional components of displacement at these sites range
from 12.4 ± 0.6 m to 49.0 ± 2.5 m toward N65°E. By combining probability density
functions of these displacements and ages, we find that extension rates averaged over late
Pleistocene–Holocene time vary from 0.1 ± 0.1 mm/yr at Furnace Creek and 0.3 ± 0.2
mm/yr at Wildhorse Creek in the south, to 0.7 +0.3/–0.1 and 0.5 +0.2/–0.1 mm/yr at
Perry Aiken Creek and Indian Creek, respectively, to the north.
These rates suggest that the Fish Lake Valley fault accommodates approximately
half of the region-wide current rate of extension measured geodetically. When summed
with extension rates on faults along the western White Mountains piedmont, the Sierra
Nevada frontal fault, and distributed deformation across the Volcanic Tablelands, the
long-term geologic rates of extension are commensurate with the short-term rates
determined from GPS data.
The increase in the east-northeast–west-southwest extensional component of slip
toward the northern end of the Eastern California shear zone reflects a gradual
northeastward transfer of slip off the predominantly right-lateral Fish Lake Valley fault
and across the Mina Deflection as part of a distributed zone of northeast-trending normal
64

faulting. Further north, in the Mina Deflection proper, deformation is accommodated
predominantly by east-west left-lateral faults (e.g., Wesnousky, 2005a). Collectively, the
distributed normal faulting in northern Fish Lake Valley, together with clockwise
rotations and motion on the east-west left-lateral faults of the Mina Deflection, serves to
transfer deformation through this major right step in the Eastern California shear zone–
Walker Lane belt.

65

CHAPTER 3:
Constancy of Geologic Slip Rate Along the Central Garlock Fault: Implications for
Strain Accumulation and Release in Southern California

3.1 Abstract
The tectonic role of the left-lateral Garlock fault in relationship to the eastern
California shear zone (ECSZ) and Pacific-North America plate boundary deformation
remains a geologic enigma. Geodetic studies imply that the majority of present-day
elastic strain accumulation occurs on strike-slip faults oriented northwest-southeast as
part of the ECSZ, almost normal to the orientation of the Garlock fault, while strain
accumulation parallel to the Garlock fault is minimal. Yet, a large number of offset
alluvial landforms at many locations along strike of the fault are suggestive of higher
tectonic activity than what geodetic strain accumulation rates imply. Combining a
LiDAR-based offset measurement of an incised channel with cosmogenic nuclide
10
Be
ages from the incised alluvial fan surface at site 449100 on the north slope of the Summit
Range, yields a late Pleistocene-Holocene slip rate of 5.0 +1.2/-2.0 mm/yr. This rate is in
agreement with previously determined geologic slip rates; however, it is at least twice as
fast as geodetically derived slip rates for the central part of the Garlock fault. Such a slip
rate discrepancy suggests that the Garlock fault is currently experiencing a period of
transient lack of strain accumulation, in which the lower crust (and mantle?) beneath the
fault is deforming at a rate that is much slower than its long-term average rate. These
observations suggest that the Garlock fault experiences two modes of strain
accumulation; the current ―slow‖ mode, in which strain accumulates very slowly along
the fault, and ―fast‖ modes, during which the fault must store elastic strain energy at
66

much faster rates than the long-term average in order to account for the relatively rapid
geologic slip rates measured along the central part of the fault. Other hypotheses have
been proposed in an attempt to explain this slip rate difference but no consensus has been
reached thus far. The findings from this study cannot disprove any of these hypotheses
but it rather provides additional evidence of constant strain release along strike in the
central part of the Garlock fault over a Holocene-late Pleistocene time scale. Such a
geologic slip rate consistency further confirms the discrepancy between strain
accumulation and strain release rates on the Garlock fault.

3.2 Introduction
One of the most fundamentally important, yet unresolved, issues in active
tectonics is the degree to which fault loading and strain release are constant in time and
space. Although comparisons of million-year plate-boundary rates (e.g., DeMets et al.,
1990; 1994) with shorter-term data suggest that rates are relatively constant along most
plate boundaries when averaged over the entire orogen (e.g., Humphreys and Weldon,
1994; Sella et al, 2002), comparison of geodetic and geologic rate data suggest that some
faults and fault systems exhibit transient strain accumulation and release over a range of
time scales (e.g., Peltzer et al., 2001; Dawson et al., 2003; Friedrich et al., 2003; Oskin
and Iriondo, 2004; Meade and Hager, 2005; Dolan et al., 2007; Oskin et al., 2006; 2007;
McGill et al., 2009). Moreover, earthquake clustering is increasingly observed at a wide
variety of spatial and temporal scales, ranging from years to millennia, on both single
faults (e.g., Barka, 1992; Marco et al., 1996; Stein et al., 1997; Dolan et al., 1998;
67

Hubert-Ferrari et al., 2002; Friedrich et al., 2003; Dolan and Bowman, 2004; Tsutsumi
and Sato, 2009; Kozaci et al., 2011), as well as regional fault networks (e.g., Berberian,
1981; Baljinnyam et al., 1993; Jackson and McKenzie, 1984; Dolan et al., 1998; Mann et
al., 1998; Rockwell et al., 2000; Nalbant et al., 2005; Dolan et al., 2007; Manaker et al.,
2008; Ganev et al., 2010). In addition, in at least some regional fault systems, transiently
elevated strain accumulation appears to coincide with clusters of large-magnitude
earthquakes (e.g., Rockwell et al., 2000; Oskin et al., 2006; Dolan et al., 2007).
Such observations raise a number of basic questions. For example, what processes
control strain accumulation and release at time scales of both individual earthquake
cycles and over multiple cycles? Is strain release relatively constant, as might be expected
if faults are loaded steadily by plate motions? Or is strain accumulation and release
markedly non-constant, as might occur if fault loading is controlled by temporally
transient mechanisms, such as lower crustal creep pulses or feedback related to
earthquake clustering? Are transient effects limited to single faults, or small regions, or
do they occur at much larger scales and over long time intervals?
In this paper, we address these issues by determining a new slip rate along the
central part of the Garlock fault in southern California. As we discuss, determination of
this rate required consideration of not only the behavior of the fault, but also of the
climatic response of the landscape, including relationships between regional climate
changes that control the cycles of aggradation and incision of offset geomorphic features.
We then discuss the implications of these results for comparisons of geologic and
68

geodetic rates in southern California, and more generally for geologic slip rate
determinations based on offset geomorphic landforms.

3.3 Active Tectonics of the Garlock Fault: Previous Work
The Garlock fault is a major left-lateral strike-slip fault that extends in a broad arc
for 250 km eastward from the San Andreas fault to the southern end of Death Valley in
the Avawatz Mountains, and possibly even further to the east (Davis and Burchfiel, 1973;
Plescia and Henyey, 1982). The fault marks a profound geologic and physiographic
boundary between the extended Basin and Range province to the north and the un-
extended Mojave desert to the south (Davis and Burchfiel, 1973). Three potentially
complementary tectonic models have been proposed to explain the Garlock fault’s
existence: (1) it forms a conjugate fault pair with the San Andreas fault that
accommodates some of the convergence at the Big Bend section of the plate boundary
fault (Hill and Dibblee, 1953; Stuart, 1991; McGill et al., 2009); (2) it is a transform fault
between the extended Basin and Range Provence to the north and the Mojave block to the
south (Davis and Burchfiel, 1973), or (3) it is a structure that accommodates clockwise
block rotation in the northeastern Mojave desert (Humphreys and Weldon, 1994; Guest et
al., 2003).
Total documented sinistral displacement is 48-64 km (Smith, 1962; Smith and
Ketner, 1970; Davis and Burchfiel, 1973; Carr et al., 1993; Monastero et al, 1997), which
initiated sometime between 17 Ma and 10 Ma (Burbank and Whistler, 1987; Loomis and
Burbank, 1988; Monastero et al., 1997; Frankel et al., 2008). A prominent, ~2-km-wide
69

extensional left step-over in the vicinity of Koehn Lake and a ~15º change in strike south
of the Quail Mountains have been used to separate the Garlock fault into western, central,
and eastern segments (McGill and Sieh, 1991) (Figure 3.1).
Despite abundant geomorphic and stratigraphic evidence for Holocene seismic
activity, the Garlock fault has not generated any large earthquakes during historic time.
At their paleoseismologic trench site in the El Paso Mountains along the central Garlock
fault, ~30 km east of the Koehn lake step-over, McGill and Rockwell (1998) and Dawson
et al. (2003) documented evidence for six surface ruptures during the past 7,000 years.
Their data reveal markedly irregular recurrence. The most recent surface rupture at their
site, which occurred between 1450 and 1640 AD, was preceded by a temporal cluster of
three surface ruptures between 25 and 950 AD. This cluster was in turn preceded by a
long seismic lull between 2-5ka, with two older events occurring at ~ 5 ka and ~7 ka. On
the western segment of the Garlock fault, Madden and Dolan (2008) documented the
occurrence of four paleo-earthquakes at their Twin Lakes paleoseismologic site in the
Tehachapi Mountains (Figure 1). The most recent surface rupture at their site occurred
after 1450 AD, and before the historic period (i.e., before ~1800-1850 AD), and may be
the same surface rupture observed at the El Paso peaks site. Similarly, Madden and Dolan
(2008) observed a surface rupture that occurred between 40 BC and 650 AD, during the
1-2 ka cluster at El Paso Mountains. They also observed events at 770 – 360 BC and
3620 – 2040 BC. These two events occurred during the long seismic lull observed at the
El Paso Mountains site, indicating that the Garlock fault may sometimes rupture in its
entirety in large-magnitude earthquakes, or closely spaced sequences of earthquakes, but
70

Figure 3.1 Index map of the southern Eastern California shear zone and Garlock
fault. The black quadrangle in the central section of the Garlock fault indicates our
investigation area north fo Summit Range.
71

that sometimes the western and central parts of the fault behave independently, perhaps in
response to rupture termination at the Koehn Lake step-over (Madden and Dolan, 2008).
McGill and Sieh (1991) mapped small-scale offsets of geomorphic features, such
as shutter ridges, gullies, terrace risers, and alluvial fans, along the central and eastern
Garlock fault where numerous offsets are preserved. Relatively few offset measurements
are currently available from the western segment of the Garlock fault, perhaps because
this stretch of the fault lies within the Tehachapi Mountains, in contrast to the mountain-
front setting of most of the central and eastern segments of the fault. A histogram of the
small-offset data from the central section of the fault, south of El Paso Mountains, reveals
marked contrasts in displacement, with offsets ranging between 7 m in the two most
recent events, and an offset of 4 m in the ante-penultimate event (McGill and Sieh, 1991).
To the east, however, along the easternmost 90 km of the Garlock fault, small-scale
offsets suggest 2-3 m of left-lateral slip during the most recent earthquake (McGill and
Sieh, 1991).
Several studies report late Pleistocene-Holocene slip rates from the Garlock fault
that range between 4 and 11 mm/yr with an emerging slip rate consensus of 5-7 mm/yr
(e.g., Clark and Lajoie, 1974; McGill and Sieh, 1993; McGill et al., 2009). Specifically,
Clark and Lajoie (1974) measured an offset shoreline berm along the margin of Koehn
Lake and dated offset tufa deposits using
14
C geochronology. Their slip rate of 4.5-6.1
mm/yr is considered a minimum since the tufa was deposited at some undetermined time
prior to the offset. McGill and Sieh (1993) obtained a well-constrained slip rate of 4-9
mm/yr, with a preferred rate of 5-7 mm/yr, using an offset late Pleistocene shoreline of
72

Searles Lake and correlation of lake stands with radiocarbon dating of organic sediments
from cores. At Clark Wash, a site along the western section of the Garlock fault about 20
km west of Koehn Lake, McGill et al (2009) reported a slip rate of 5.3-10.7 mm/yr based
on an offset incised channel and radiocarbon age dating. These geologic slip rates are not
significantly different than the geologic rates based on offset features that are millions of
years old. Carter et al. (1994) determined a slip rate of 5.5-8 mm/yr by dating early
Hemphillian fossils (6-9 Ma) recovered from the offset Bedrock Springs Formation,
whereas Burbank and Whitsler (1987) and Loomis and Burbank (1988) inferred that
progressive sinistral rotations of the Ricardo Group in the southwestern El Paso
Mountains between 10 Ma and 7 Ma indicate the initiation of sinistral slip on the Garlock
fault. This initiation age, combined with the 64-km total displacement on the Garlock
fault, would yield a slip rate of 6-9 mm/yr. Additionally, Monastero et al. (1997) and
Keenan (2000) reported on 17 Ma Miocene rocks that may be the youngest rock units to
exhibit the full fault displacement, which would yield a minimum slip rate of >3.8
mm/yr.
Such geologic slip rates, however, are inconsistent with most geodetically derived
short-term slip rates on the Garlock fault, which indicate sinistral slip rates that are no
more than half the geologic slip rates (McClusky et al., 2001; Miller et al., 2001; Peltzer
et al., 2001; Meade and Hager, 2005). Instead, these geodetic studies reveal a velocity
field dominated by northwest-oriented, right-lateral shear parallel to the eastern
California shear zone, and extending across the Garlock at a high angle. Such a shear
zone could be related to the temporal and spatial clustering of earthquakes along the
73

Garlock fault (Peltzer et al., 2001; Dolan et al., 2007); however, the precise nature of the
relationship between the Garlock fault and the northwest-oriented, right-lateral faults of
the ECSZ remains unknown.

3.4 Summit Range Study Area
The central part of the Garlock fault, east of Koehn Lake and west of the Quail
Mountains, is relatively structurally simple; for the most part, it exhibits a single, east-
northeast-striking fault strand within Holocene deposits, with local subordinate parallel
strands, most of which accommodate dip-slip (mainly reverse) motion (Figures 3.2 and
3.3). This relative structural simplicity, coupled with the mountain front location of the
fault trace along this reach, results in well-defined sinistral offsets of numerous
geomorphic features (e.g., rills, incised stream channels, alluvial fans), with offsets
ranging in scale from a few meters to >500 m (Clark, 1973; McGill and Sieh, 1991).
We used the recently acquired GeoEarthScope LiDAR data set to examine an
especially promising, 7-km-long stretch of the Garlock fault located along the northern
edge of the Summit Range east of Trona Road, where offsets of several tens of meters are
particularly prominent and well-preserved (Figure 3.2). Several of these sites were
previously identified by Clark (1973). In this region, the Garlock fault strikes ~080° and
offsets mostly Upper Quaternary alluvial deposits rather than bedrock. In the 7-km-long
stretch that we studied, we identified at least four offset channels that are displaced 65-70
m, whereas several channels and an alluvial fan are displaced by 40-50 m (Figure 3.3).
The alluvial deposits, consisting mostly of sand, pebble gravel, and silt, are transported
74

Figure 3.2 Map of the central part of the Garlock fault. The black quadrangle outlines our study area. ALF-
Airport Lake fault, cGF- central Garlock fault, PVF- Panamint Valley fault, SNF- Sierra Nevada Frontal
fault, wGF- western Garlock fault.
75

Figure 3.3 (A) Annotated LiDAR image of our study site and the vicinity. The
location of Figure 3.3 is outlined by the white dashed line. (B) Aerial
photograph of the same area as in (A). (C) Topographic map (5m interval)
derived from the LiDAR dataset of the same area as in (A).
76

northward from the northern slopes of the Summit Range towards the lowest parts of the
adjacent valley, which is bounded by the Summit Range to the south, the Spangler Hills
to the north and the Slate Range to the east. Relatively small bedrock outcrops are present
at several locations on the Summit Range side of the valley (unit QTc in Figure 4). We
suspect these are either part of the Bedrock Springs Formation or are younger gravels
derived from that formation.
One of the most prominent offset landforms that we examined with the LiDAR
data is a sharply offset incised stream channel located at 35º28’44.9‖N and
117º33’36.73‖W (Figure 3.4). We informally call this the ―channel 449100‖ site, after the
UTM easting of this offset. The active stream that flows northward through the offset is
one of the main channels that drain the central part of the Summit Range. The channel is
incised into several abandoned alluvial fan deposits that also emanated from this source
drainage. The abandoned alluvial fan surfaces are moderately well-preserved, with
limited erosion near the edges formed by the incised channels; however, anthropogenic
disturbances (all-terrain-vehicle tracks) are prominent at certain locations. The offset
channel is incised into deposits Qoa and Qf3 (Figure 3.4) which formed during late
Pleistocene periods (see ―TCN Geochronology‖ section below) of alluvial fan
aggradation. Qoa, a deposit of granitic origin, with clasts no bigger than 5 cm in
diameter, oxidized grains, and subdued relief, is the predominant deposit at the site. Qf3
is a deposit of granitic origin found on each side of the offset channel, representing a
small alluvial fan deposited only locally. It consists of 10-30 cm granitic clasts, which are
well-cemented in a carbonate matrix in the bottom ~10-20 cm of the unit. The channel
77

Figure 3.4 (A) Map of Summit Range site with the mapped Quaternary deposits. (B) Retrodeformed map of
the Summit Range site. Restoration of displacement is based on the Qf3 surface indicated by the light orange
color.
78

that is incised into these two deposits provides the opportunity to observe the
stratigraphic relationship between Qoa and Qf3. The Qf3 deposit is no more than 3 m
thick and it overlies Qoa on both sides of the channel.
3.4.1 Fault Displacement
The LiDAR data (available online at http://www.opentopography.com) collected
along the Garlock fault north of the Summit Range show the prominent sinistral offset of
the main channel (449100), as well as a set of another six deflected channels to the east
that are incised into the older Qoa surface (Figure 3.4-3.6). The sinistral offsets are
largely localized along a single strand, although two south-dipping reverse fault strands
are also present. These reverse strands do not appear to contribute any significant amount
of lateral slip to the total fault displacement. The six deflected channels merge into the
main stream about 200-300 m north of the fault, as the main stream changes flow
direction towards northeast due to the presence of the QTc outcrop (Figure 4). These
channels are incised into the older Qoa deposit, and therefore we focus on the offset
channel which incised through the younger Qf3 deposit. The channel displacements were
measured in ArcGIS (version 9.2) directly from the digital elevation model (DEM)
derived from the LiDAR dataset.
The geomorphic offset of channel 449100 was previously estimated at ~45 m
(reported as 150 ft), based on the offset of the channel thalweg (Clark, 1973). Our new
data reveal a more complicated fault offset history of this site. Preservation of the edge of
the Qf3 alluvial fan surface along the western edge of channel 449100 both north and
south of the fault allows us to determine the offset since initial incision of the Qf3 fan
79

Figure 3.5 Panoramic view looking south towards the Summit Range.
80

Figure 3.6 View overlooking the Summit Range site. Note the 54 ± 4 m left-lateral
displacement of the incised channel.
81

surface. Restoration of 70 m of sinistral offset yields a plausible configuration of the
locus of initial channel incision into the Qf3 surface following fan abandonment. We
estimate conservative errors on this measurement of ± 7 m based on the fact that
restoration of 77 m closes off any northward flowing channel incised into the Qf3
surface, and restoration of 63 m results in a sedimentologically unlikely ―backwards‖
bend to the west of the Qf3 surface edge at the fault.
Our preferred restoration of 70 m, however, does not restore the deeply incised
thalweg of channel 449100, as shown in Figure 3.7. Specifically, at a restoration distance
of 70 m, the thalweg of the channel exhibits a pronounced and sedimentologically
unlikely ~10 m deflection to the right at the fault crossing. Our preferred restoration of
the deeply incised channel thalweg is 58 ± 4 m. This restoration yields a gently curved,
sedimentologically plausible configuration for the incised channel with a minimum of
channel curvature at the fault. The fact that the edge of Qf3 surface, which we interpret as
recording initial shallow incision upon abandonment at ~13.3 ka yields a different
preferred restoration (70 ± 7 m) from the deeply incised thalweg (preferred restoration of
58 ± 4 m) indicates that these features record different events that developed at different
times.

82

Figure 3.7 Slip restorations of various amounts (B-H) in increments of 5
m. Best restoration for the initial incision is at 70 ± 7 m (based on
restoring the edge of surface Qf3 west of the channel), whereas a
restoration of the thalweg (interpreted as a younger incision) yields a
displacement of 58 ± 4 m. White dashed line in (A) outlines location of
(B-H).
83

3.4.2 TCN Geochronology
We quantified the ages of Qoa and Qf3 alluvial fan surfaces by measuring the
concentration of in-situ produced terrestrial cosmogenic nuclide (TCN)
10
Be samples
collected from depth profiles through the top ~2 m of the deposits (e.g., Lal, 1991; Gosse
and Phillips, 2001). Beryllium-10 is a radioactive isotope that is produced through
spallation and muon-induced reactions with Si and O in quartz (Gosse and Phillips,
2001). Estimation of the inherited component of
10
Be is of critical importance for
accurate determination of the age of abandonment of the fan surface. The concentration
of TCN diminishes quasi-exponentially with depth beneath the surface (Anderson et al.,
1996; Gosse and Phillips, 2001), and therefore a model surface age can be extrapolated to
0 cm depth from the
10
Be concentration versus depth curve (e.g., Anderson et al., 1996;
Hancock et al., 1999; Hidy et al, 2010). Because the concentrations of
10
Be below 2 m
should be negligible, the inheritance in the deposit can also be determined from a depth
profile (e.g., Anderson et al., 1996).
We collected samples from two pits excavated into the Qoa deposit and one pit
excavated into the Qf3 deposit. The ~2-m-deep pits were hand excavated at locations
where the original fan surface was best preserved, and far removed from any obvious
erosional features. Samples were collected from depths of 1.9 m, 1.5 m, 1.2 m, 0.9 m, 0.6
m, and 0.3 m below the fan surface. The samples, which were processed at the Georgia
Institute of Technology Cosmogenic Nuclide Geochronology Laboratory, were first
crushed, then ground and sieved to a grain fraction of 250-750 µm. Following the
procedures described in Kohl and Nishiizumi (1992), quartz was first isolated, Beryllium
84

was extracted from the samples by ion exchange chromatography, precipitated as
Be(OH)
2
, and oxidized to BeO (e.g., Bierman et al., 2002). After ignition of the BeO, the
samples were then mixed with Niobium and packed in stainless-steel cathodes. The
amounts of
10
Be/
9
Be were measured at the Lawrence Livermore National Laboratory
Center for Accelerator Mass Spectrometry, and
10
Be model ages were subsequently
determined using the CRONUS-Earth online calculator, version 2.2
(http://hess.ess.washington.edu; Balco et al., 2008). Currently, there is no consensus in
regards to which time-variant production-rate model is most accurate (e.g., Lal, 1991;
Stone, 2000; Dunai, 2001; Desilets and Zreda, 2003; Pigati and Lifton, 2004; Desilets et
al., 2006; Lifton et al., 2005; Balco et al., 2008; Staiger et al., 2007). Therefore, we chose
to use a time-invariant production-rate model to determine the ages of the deposits (Lal,
1991; Stone, 2000). We used the methodology and Monte Carlo simulator developed by
Hidy et al. (2010) (available online at
http://geochronology.earthsciences.dal.ca/downloads-models.html) to perform 100,000
Monte Carlo simulations to determine the best-fitting depth profiles based on the
parameters outlined in Table 3.1.
3.4.3 TCN Results
3.4.3.1 Qf3
Depth profile PG1209 constrains the age of abandonment of the Qf3 fan surface
(Figure 5a). Hidy et al.’s (2010) model, which we used to determine the surface age,
incorporates site-specific geologic knowledge (e.g., altitude, latitude, shielding) to
calculate the most probable values for exposure age, erosion rate, and inherited nuclide
85

concentration. In addition, the model permits an explicit propagation of all error sources
of those variables. One requirement of this depth-profile technique is that inheritance
must be considered constant over the depth range of the processed samples (Anderson et
al., 1996), although this may not be the case where deposition is incremental over long
time periods, where depositional processes vary in the profile, and where catchment-wide
erosion rates differ significantly during the span of deposition.
The Qf3 calculated age is, therefore, based on the best-fit curve through six
samples collected between 1.9 m and 0.3 m below the surface. The resulting best-fit
10
Be
model age is 13.3 +5.9/-1.0 ka, and the inheritance is 1.35 +0.06/-0.09 x 10
5
atoms/g
SiO
2
(Figure 3.8). Thus, the Qf3 surface was abandoned at ~ 13 ka, providing a
maximum age for the initial incision of the offset channel that we use to calculate the slip
rate at the Summit Range study site.
These results are consistent with the record of major climate changes in the
Mojave region. Specifically, major drying occurred at the onset of the Younger Dryas
(13-11.5 ka) in the Mojave region and elsewhere throughout western North America and
the rest of the Northern Hemisphere (e.g., Mott et al., 1986; Johnsen et al., 1992;
Edwards et al., 1993; Peteet, 1995; Osborn, 1995; Kennet and Ingram, 1995; Lowell et
al., 1995; Benson et al., 1997; Mikolajewicz et al., 1997). The onset of this relatively dry
period at ~13 ka terminated extensive alluvial fan aggradation throughout the region
(VanDevender and Spaulding, 1979; Benson et al., 1997, Benson et al., 1998). We
observe evidence for this event in the 13 ka age on our Qf3 surface, which records
abandonment of this fan surface. A similar age for fan abandonment is observed 60 km to
86

the west-southwest at McGill et al.’s (2009) Clark Wash site, where fan aggradation
processes continued to at least 13.3 ka. Thus, the major impact of the onset of the
Younger Dryas period was cessation of fan deposition throughout the Mojave at ~ 13 ka.
Thus, the 13.3 ka abandonment age provided by the Qf3 depth profile at our channel
449100 site is consistent with the idea of a cessation of alluvial deposition at the site and
abandonment of the Qf3 surface at the onset of the Younger Dryas period.

87

Figure 3.8 Be-10 cosmogenic nuclide depth profiles from deposits: (A) Qf3-
location: 35º28’42.2”N/ 117º33’34.1”W; (B), Qoc- location: 35º28’48.5”N/
117 º33’38.7”W; and (C) Qoc- location: 35º28’50.98”N/ 117º33’19.85”W.
88

89

3.4.3.2 Qoa
Depth profiles from two locations constrain the timing of abandonment of the Qoa
surface (Figure 3.8). Although we collected six samples in a depth profile (PG0110)
extending down to 200 cm depth, the bottom three samples were located below a ~20-
cm-thick carbonate-cemented layer located 100 cm below the surface. We interpret this
layer as moderately well-developed (Stage I+) Bk paleosol that records a period of fan
abandonment and pedogenisis that was superseded by renewed deposition of the
uppermost meter of alluvial fan sediment and subsequent re-abandonment of the fan.
Thus, the exposure histories of the older and younger fan material will record different
10
Be concentrations. In an attempt to determine the age of the Qoa surface, we used only
the top three samples because of the extreme discordance with the theoretical change in
nuclide concentration with depth ( the
10
Be concentrations of the lower three samples are
shown in Data Repository). The
10
Be model age for depth profile PG0110 is 36.2 +41.5/-
19.6 ka (inheritance is equal to 0.78 +0.97/-0.68 x 10
5
atoms/g SiO
2
) based on only the
top three samples. Since the model requires at least four samples to statistically determine
a surface age while not violating the assumption that inheritance is constant with depth
(Hidy et al., 2010), we note that the age of profile PG0110 is not well-constrained.
The model age of depth profile PG0410 is 43.8 +42.8/-27.9 ka (inheritance is
equal to 0.97 +0.73/-0.64 x 10
5
atoms/g SiO
2
) based on the best-fit curve through five
samples. The top sample, located 0.3 m below the surface, yielded a much lower
concentration, which we suspect is due to mixing of sediment. The removal of the top
sample from the dataset allows for a wide range of surface exposure ages, which is
90

reflected in the large error limits for the age. Because of the complicated depositional and
exposure history of the Qoa deposit at PG 0110, and the wide spread in sample ages at
PG0410, the resulting
10
Be ages are poorly constrained. Nevertheless, these results
indicate that the Qoa surface was abandoned several tens of thousands of years ago, most
likely at 30-40 ka (range, 15-80 ka).
As with the Qf3
10
Be results, the results of the Qoa depth profiles are broadly
consistent with paleoclimate observations from the Mojave region. Specifically, during
latest Pleistocene time (30-13 ka), a major aggradational pulse is observed from Clark
Wash (McGill et al., 2009) 60 km west-southwest of our site, to Soda Lake basin (Harvey
and Wells, 2003), Soda Mountains (Wells et al., 1987, 1990) and Providence Mountains
(McDonald et al., 2003), 150-200 km to the east of our site. During this period, fluvial
and sheet-flood processes formed relatively large alluvial fans throughout the region. At
the Summit Range site, although not well-constrained, we observe a similar period of
extensive alluvial fan aggradation recorded by the wide-spread deposition of the Qoa
deposit, which we interpret as being deposited at ~40 ka (model age from depth profile
PG0110 is 36.2 +41.5/-19.6 ka, and from PG0410 is 43.8 +42.8/-27.9 ka). This alluvial
fan unit could potentially be equivalent to unit Qf1 at Soda Lake basin, whose age based
on soil-profile development is 30-18.6 ka (Harvey and Well, 2003).

91

3.5 Latest Pleistocene-Earliest Holocene Fault Slip Rate
3.5.1 Minimum Rate Based on Fan Abandonment Age
Combining the 70 ± 7 m preferred offset of the well-preserved edge of the Qf3
fan surface along the western wall of channel 449100 with the 13.3 +5.9/-1.1 ka
abandonment age of the incised Qf3 surface yields a fault slip rate 5.3 +1.0/-2.0 mm/yr.
This rate, however, should be considered a minimum for several reasons. Firstly, the rate
is based on the assumption that incision of the channel into the Qf3 surface began
immediately upon fan abandonment at ~13 ka. If, however, channel incision actually
occurred significantly later than fan abandonment at ~13 ka, the resulting rate would be
faster. Secondly, although we are confident on the basis of our LiDAR-based and field
geomorphic mapping that almost all of the fault slip occurs along the main strand, there is
evidence for some minor (probably mostly reverse) faulting parallel to and north of the
main strand along the northern edge of the Summit Range (Figure 4A). Finally, as with
all surface faulting, some minor, geomorphically undetectable distributed near-surface
slip may have occurred.
3.5.2 Possible Maximum Rate Based on Paleoclimate Considerations
As noted above, the deeply incised thalweg of channel 449100 is offset 58 ± 4 m,
significantly less than the preserved edge of the Qf3 fan surface along the western edge
of the channel, which is offset 70 ± 7 m. This geometry indicates that the main incision
event that resulted in the current, deeply incised channel occurred after approximately 10-
15 m of Garlock fault sinistral offset had accumulated following abandonment of Qf3.
Inasmuch as the incision was probably controlled by climate change, we have examined
92

the climate literature for latest Pleistocene-early Holocene changes in the Mojave region
for possible causative events. We suggest two possible climate-based scenarios for the
age of the deep incision event. The end of Younger Dryas period at 11.5 ka resulted in a
generally wetter climate in the desert southwest, suggesting the possibility that deep
incision began during the return to post-Younger Dryas wetter conditions (e.g., Mott et
al., 1986; Johnsen et al., 1992; Edwards et al., 1993; Peteet, 1995; Osborn, 1995; Kennet
and Ingram, 1995; Lowell et al., 1995; Benson et al., 1997; Mikolajewicz et al., 1997). If
the main incision event for channel 449100 occurred at ~11.5 ka, this would result in a
slip rate of ~5.0 ± 0.4 mm/yr. Alternatively, the most pronounced climate change in the
region following the end of the dry conditions prevailing during the Younger Dryas at
~11.5 ka occurred between 10 and 8 ka, when summer monsoonal rainfall patterns were
initiated (e.g., King, 1976; Spaulding and Graumlich, 1986; VanDevender et al., 1987;
Wells et al., 1987, 1990; Bull, 1991; McDonald et al., 2003; Harvey and Wells, 2003).
Based on this, we suggest the possibility that the deep incision event at channel 449100
may have occurred as recently as 10-8 ka. If correct, the 58 ± 4 m offset of the deeply
incised thalweg, combined with the 10-8 ka age of onset of the wet summer monsoon
weather pattern, would yield a slip rate of 6.6 +/- 1.2 mm/yr, slightly faster than the
minimum rate we infer from abandonment and initial incision of the Qf3 surface.

93

3.6 Discussion
3.6.1 Geologic Slip Rate Comparisons From the Garlock Fault
Our minimum ~13.3 ka Garlock fault slip rate of 5.3 +1.0/-2.0 mm/yr based on
the abandonment age of the Qf3 surface, and our alternative slightly younger slip rates
based on the timing of deep incision of channel 449100 (5.0 ± 0.4 mm/yr [11.5 ka] and
6.6 ± 1.2 mm/yr [8-10 ka]) are in general agreement with most previously determined
geologic slip rates, including other late Pleistocene-Holocene rates and longer-term
Miocene rates (Figures 3.9). For example, Carter et al. (1994) determined a slip rate of
5.5-8 mm/yr based on the offset of 6-9 Ma Bedrock Springs Formation, while Burbank
and Whistler’s (1987) and Loomis and Burbank’s (1988) suggested 7-10 Ma age of
initiation of Garlock fault slip yields a slip rate of 6-9 mm/yr, based on a cumulative fault
displacement of 48-64 km (Smith, 1962; Smith and Ketner, 1970; Davis and Burchfiel,
1973; Monastero et al, 1997). Similarly, published late Pleistocene- Holocene slip rates
range from 4-9 mm/yr, with a preferred slip rate range of 5-7 mm/yr (Clark and Lajoie,
1974; McGill, 1992; McGill and Sieh, 1993; McGill et al., 2009). These late Pleistocene-
Holocene slip rates were measured at multiple sites spanning a 100 km length of the
Garlock fault, from the eastern portion of the western Garlock fault at Clark Wash
(McGill et al., 2009), through the Koehn Lake stepover (Clark and Lajoie, 1974), and our
study site in the Summit Range, and eastward to Searles Lake (McGill, 1992; McGill and
Sieh, 1993).
The similarity of these rates suggests remarkably consistent displacement along
the Garlock fault during latest Pleistocene-Holocene time. We note, however, that all of
94

Figure 3.9 Locations of slip-rate sites along the Garlock fault. Values in black
are Holocene or latest Pleistocene rates, summarized in the table below the map.
The three values in white are the slip rates and uncertainties from Meade and
Hager’s (2005) elastic block model that best fits the available geodetic data.

95

these rates are averaged over many earthquake cycles, and shorter term paleoseismologic
data suggest the possibility that the Garlock fault slip rate may not always be consistent
over time scales spanning fewer earthquake cycles. Specifically, Dawson et al. (2003)
report four earthquakes (events W, U, R, and Q) which occurred between A.D. 1450-
1640 and A.D. 25-275. A histogram of small-scale offset measurements from the El Paso
Mountains (McGill and Sieh, 1991) reveals peaks at 7 m, 14 m, and 18 m, suggesting
cumulative offsets in the past one, two, and three events that sum to these values. Dawson
et al. (2003) used these data to infer displacements at their El Paso Peaks trench site of 7
m, 7 m, and 4 m, for the three most recent surface ruptures at their site. If we use this
same inference, we can use the paleo-earthquake ages and inferred displacements to
calculate a geologic slip rate averaged over the short period represented by the past three
earthquakes. The cumulative slip in the past three earthquakes is 18 ± 2 m (McGill and
Sieh, 1991). This strain accumulated over the time interval between events Q (25-275
C.E.) and W (1450-1640 C.E.) at the El Paso Peaks site (Dawson et al, 2003). Dividing
the cumulative slip by this 1175- to 1615-year time interval yields a slip rate of 13 ± 2
mm/yr. This could indicate that the Garlock fault has been in a period of enhanced
activity for the past 2 ka.
Alternatively, the 7-m and 14-m offsets measured by McGill and Sieh (1991) at
El Paso Peaks may represent cumulative slip in the past two and the past four
earthquakes, respectively. In Searles Valley, ~20 km east of the El Paso Mountains,
McGill and Sieh (1991) report displacements in the most recent event that average 2 ±
0.5 m. Similarly, in Pilot Knob Valley, ~ 50 km east of the Dawson et al. (2003) trench
96

site, McGill and Sieh (1991) report peaks in cumulative displacements in past events at
3.4 m, 5.3 m, and 8.6 m, indicating offsets in the past three surface ruptures of ~3.5 m, ~2
m, and ~3.5 m. Based on these much smaller displacements measured to the east of the El
Paso Mountains, an alternative interpretation of the small-offset data is that slip along the
central part of the Garlock fault is typically on the order of 2-4 m, and that the 7 m
displacements observed in the El Paso Mountains area reflect rates of incision of new
drainages that are slower than the repeat time of surface ruptures, as suggested recently
for the central San Andreas fault by Grant Ludwig et al. (2010) and Zielke et al. (2010).
In other words, the 7 m offsets observed by McGill and Sieh (1991) near the Dawson et
al. (2003) trench site may each record slip in more than one earthquake. This would result
in a slower geologic slip rate measurement. For example, if slip in the past three
earthquakes observed at the El Paso Mountains site was only 3.5 m each (assuming 7 m
of displacement records two events), then the short-term geologic slip rate of the fault
would be ~6-9 mm/yr (3 events x 3.5 m per event = 10.5 m, divided by 1175-1615 yr).
More short-term slip-rate data are required, however, before drawing any firm
conclusions about whether or not the Garlock fault has had an elevated slip rate over the
past ~2 ka.
3.6.2 Geologic VS. Geodetic Slip Rate Comparisons From the Garlock Fault
Geodetic measurements of the rate of elastic strain accumulation on the Garlock
fault have consistently indicated rates that are significantly slower than geologically
determined slip rates (e.g., Figures 3.9-3.10; McClusky et al., 2001; Peltzer et al., 2001;
Miller et al., 2001; Meade and Hager, 2005). For example, Meade and Hager (2005) used
97

Figure 3.10 Compilation of slip rates from the Garlock fault on a time vs. slip-
rate graph. Upward and downward arrows indicate minimum and maximum slip
rates, respectively. White hexagons indicate preferred slip rates as indicated by
the authors of each publication, while white polygons indicate the ranges of
preferred slip rates as indicated by the authors of those publications. The slip
rates come from the following sources: a- Meade and Hager (2005); b- McClusky
et al. (2001); c- Miller et al. (2001); d- based on age data from Dawson et al.
(2003); e- Clark and Lajoie (1974); f- McGill et al. (2009); g- this study; h- McGill
and Sieh (1993); i- Carter et al. (1994); j- Burbank and Whistler (1987), Loomis
and Burbank (1988); k- Keenan (2000); l- Monastero et al. (1997).
98

an elastic block model constrained by Global Positioning System measurements of
interseismic deformation to determine a rate of elastic strain accumulation along the
central Garlock fault of 1.8 ± 1.5 mm/yr. This rate is much slower than the 5-7 mm/yr
geologic slip rates measured along the central section of the fault, suggesting that the
Garlock fault is currently experiencing a period of transient strain accumulation, in which
the lower crust (and mantle?) beneath the fault is deforming at a rate that is much slower
than its long-term average rate. These observations suggest that the Garlock fault
experiences two modes of strain accumulation; the current ―slow‖ mode, in which strain
accumulates very slowly along the fault, and alternating ―fast‖ modes, during which the
fault must store elastic strain energy at much faster rates than the long-term average in
order to account for the relatively rapid geologic slip rates measured along the central
part of the fault.
Multiple hypotheses have been proposed in an attempt to explain this slip rate
difference but no consensus has been reached thus far. One of those ideas calls for
switching of seismic activity between the fault networks of the eastern California shear
zone and the Garlock and San Andreas fault systems (Peltzer et al., 2001; Dolan et al.,
2007) due to fluctuations in the loading rate at depth associated with cycles of strain
hardening and annealing (Dolan et al., 2007). Another idea suggests northeast-trending,
sinistral strain release driven by northwest-trending, dextral strain accumulation (e.g.,
Savage et al., 2001; McGill et al., 2009), which results in conjugate faulting between the
Garlock and San Andreas faults (Hill and Dibblee, 1953; McGill et al., 2009). The
findings from this study cannot distinguish between these potentially complementary
99

hypotheses. Rather, they provide additional evidence of constant strain release along
strike in the central part of the Garlock fault over a Holocene-late Pleistocene time scale.
This along-strike consistency further highlights the discrepancy between strain
accumulation and strain release rates on the Garlock fault.

3.7 Conclusions
A
10
Be depth profile age for abandonment of a small alluvial fan in the Summit
Range that crosses the central Garlock fault, combined with LiDAR- and field-based
mapping of a stream incised into the abandoned fan, yields a minimum latest Pleistocene-
Holocene slip rate of the central Garlock fault of 5.3 +1.0/-2.0 mm/yr, and a possible
maximum rate based on offset of the deeply incised channel thalweg and climate
considerations of ~6.6±1.2 mm/yr. These rates are similar to other late Pleistocene-
Holocene rates measured along a 100-km-long section of the central Garlock fault,
highlighting the spatial consistency of slip along this part of the fault system when
averaged over 10
5
year time scales. These relatively consistent latest Pleistocene-
Holocene rates, however, are much faster than the current rate of elastic strain
accumulation from geodetically constrained block models, indicating that the Garlock
fault is currently experiencing a strain transient in which the lower crust (and mantle
lithosphere?) beneath the fault are deforming much more slowly than the long-term
average rate. If correct, this observation implies that the Garlock fault experiences two
modes of strain accumulation, with the fault currently in a ―slow‖ mode. Such slow
modes, however, must be balanced by periods of commensurately faster strain
100

accumulation. The available geologic slip rates, including that documented in this paper,
all average slip along the fault over 10
5
year time scales. This observation, coupled with
the fact that the ~ 10 ka fault slip rates generally match much longer-term (6-9 Ma)
Garlock fault slip rates based on bedrock offsets, suggests that any ―fast‖ periods of
elastic strain accumulation probably occur at shorter time scales, on the order of only a
few earthquake cycles. Combining the small-scale displacement data (McGill and Sieh,
1991) with paleoseismologic data (Dawson et al., 2003) from the El Paso Peaks area 20
km west of our study site suggests that the slip rate of the central Garlock fault may have
been much faster (13±2 mm/yr) than the long-term average during a cluster of four
earthquakes that occurred between ~25 AD and 1650 AD, perhaps reflecting an elevated
rate of elastic strain accumulation. Additional, shorter-term slip rate data, however, will
be required to confirm this suggested association between earthquake clustering and
elevated slip rate.

101

CHAPTER 4:
Paleoseismologic Evidence for Multiple Holocene Earthquakes on the Calico Fault:
Implications for Earthquake Clustering in the Eastern California Shear Zone

4.1 Abstract
Paleoseismologic data from trenches excavated across the Calico fault in the
Eastern California shear zone reveal evidence for four surface ruptures during the past
~9000 yr. Twelve optically stimulated luminescence dates constrain the timing of these
surface ruptures, which are defined by the geometry of growth strata, fissure fills, and
upward fault terminations, to 0.6–2.0 ka, 5.0–5.6 ka, 5.6–6.1 (or possibly 7.3) ka, and 6.1
(or 7.3) to 8.4 ka. Geomorphologic mapping of the 8 km section of the fault extending
southward from the trenches reveals two sets of displacements that record the slip from
the past two or three surface ruptures. The slip caused by the most recent event was ~2.0
m, while the cumulative slip during the penultimate (and possibly the antepenultimate)
event was ~4.5 m. The ages of the paleoearthquakes coincide with periods of clustered
moment release identified previously on other faults in the Eastern California shear zone
at 0–1.5 ka, 5–6 ka, and ca. 8–9.5 ka, with two Calico fault surface ruptures occurring
during the 5–6 ka Eastern California shear zone cluster. These data strongly reinforce
earlier suggestions that earthquake recurrence in the Eastern California shear zone is
highly clustered in time and space. Such seismic clustering suggests that at least some
regional fault networks undergo distinct periods of systemwide accelerated seismic
moment release that may be driven by feedbacks between fault-loading rate and
earthquake activity.

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4.2 Introduction
There is a growing body of evidence that earthquakes cluster at a wide variety of
spatial and temporal scales over both individual faults and regional fault networks (e.g.,
Ambraseys, 1971; Marco et al., 1996; Dolan and Wald, 1998; Rockwell et al., 2000;
Friedrich et al., 2003; Dawson et al., 2003; Weldon et al., 2004; Dolan et al., 2007).
Documentation of the temporal and spatial scales over which clustering occurs is
important for developing tectonic models for accurate seismic hazard assessment (e.g.,
probabilistic seismic hazard analysis [PSHA]). Moreover, an understanding of the
mechanisms for clustering would contribute to a deeper understanding of earthquake
physics and the geodynamics of the lithosphere.
The Calico-Blackwater fault system is the longest in the Mojave section of the
Eastern California shear zone, a set of predominantly north-to northwest-striking dextral
faults that trends northward from the San Andreas fault, across the Mojave Desert, and to
the east of the Sierra Nevada (Figure 4.1). Recent studies indicate a long-term slip rate
for the Calico fault of 1.8 ± 0.3 mm/yr, averaged over the past 57 ± 9 k.y. (Oskin et al.,
2007, 2008). Although this represents approximately one third of the total geologic slip
rate across the six major faults (i.e., Helendale, Lenwood, Camp Rock, Calico-
Blackwater, Pisgah, and Ludlow) that comprise the Mojave section of the Eastern
California shear zone, the paleoearthquake history of the Calico fault has not previously
been documented.
A compilation of paleoseismologic data from the majority of the faults in the
Mojave section of the Eastern California shear zone (but not including the Calico fault)
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Figure 4.1 Map showing the faults of the Eastern California shear zone in the
Mojave Desert. The Calico fault is highlighted in yellow, green star indicates the
location of the trench sites, and the green quadrangle shows our geomorphic
survey area. ALF – Airport Lake fault, B – Barstow, BF – Blackwater fault, BLF –
Bycicle Lake fault, CF – Calico fault, CLF – Coyote Lake fault, CRF – Camp Rock
fault, FIF – Fort Irwin fault, GF – Garlock fault, GLF – Goldstone Lake fault, HF
– Helendale fault, HLF – Harper Lake fault, LF – Lenwood fault, LoF – Lockhart
fault, MF – Manix fault, PF – Pisgah fault, PVF – Panamint Valley fault, SAF –
San Andreas fault, SDVF – southern Death Valley fault, TF – Tiefort Mountain
fault.
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revealed that strain release has been highly episodic over the past 12,000 yr, with
pronounced clusters of earthquakes at ca. 8–9.5 ka, 5–6 ka, and during the past ~1000–
1500 yr (Rockwell et al., 2000). The 1992 Mw 7.3 Landers and 1999 Mw 7.1 Hector
Mine earthquakes are the two most recent earthquakes of the ongoing, latest Holocene
cluster.
The lack of previous paleoseismic studies of the Calico fault thus leads to a
simple test of the clustering hypothesis. Because the Calico fault slips faster than other
nearby faults, larger or more frequent earthquakes should accommodate its slip. If
regional clustering of earthquakes modulates fault-zone activity in the Mojave Desert
section of the Eastern California shear zone, then these earthquakes should fall into the
regional clustering time periods identified by Rockwell et al. (2000). In this paper, we
describe the results of a paleoseismologic trench study and geomorphic analysis of offset
features along the northern part of the Calico fault, and discuss the implications of our
results for earthquake behavior and seismic hazard assessment.

4.3 Site Description
Our study site is located in the town of Newberry Springs, California, ~30 km east
of the city of Barstow (Figures 4.1-4.3). The ~N30°W-striking fault trace at the site is
well expressed on aerial photographs as a very low-relief (<15–20 cm high),
predominantly east-facing scarp and a pronounced vegetation lineament that extend
across the playa deposits (Figure 4.2). Two parallel fault strands, a prominent eastern
strand and a more subtle western strand, are recognizable on the surface. The sediment
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Figure 4.2 Aerial phorograph showing the surface expression of the Calico fault
(National Agriculture Imagery Program, 2005). The blue line indicates the
mappable fault trace, which creates a vegetation lineament with sparse vegetation
to the northeast. The trench sites are located on playa sediments to the northeast of
the Newberry Mountains. The photograph in Figure 4.3 is taken from the overpass
at Newberry Springs Road and National Trails Highway.
106

Figure 4.3 View southeastward toward the trench sites on the playa field. The
Calico fault trace is shown in purple. Shown in the distance is the location of Oskin
et al.’s (2007) Pleistocene slip-rate study.
107

sources are alluvial fans to the west of the site originating from the Newberry Mountains.

4.4 Paleoseismic Trenching
We excavated two fault-perpendicular trenches in the playa where the fault trace
was well expressed and where no vegetation was present to obstruct the excavation, or to
disturb the youngest strata. The northern trench was 30 m long and 0.9 m wide, with a
maximum depth of 3 m. The trench end points were located at 34°49.190′N,
116°39.697′W, and 34°49.182′N, 116°39.715′W. The length of the trench ensured that all
fault strands were exposed. A second trench (the ―southern trench‖) was excavated ~100
m to the south in order to assess the repeatability of the event chronology logged from the
northern trench. The southern trench was 15 m long and 3.5 m deep. The western 11 m of
this trench were 0.9 m wide, whereas the 3 m east of the main fault zone were 1.4 m wide
due to wall-stability problems. The end points of this trench were located at 34°49.138′N,
116°39.668′W, and 34°49.132′N, 116°39.675′W.
Both trenches exposed fluvial, lacustrine, and playa sediments consisting of well-
stratified and thinly bedded pebble gravel to coarse-grained sand, silt, and clay,
respectively (Figure 4.4). The fault zone exposed in the trenches consists of two
strands—the eastern (main) strand and a less-pronounced western strand (Figure 4.5).
Although motion on the two strands is predominantly strike slip, subordinate vertical
components of movement have created a down-dropped block between them. Total
vertical separation across the eastern fault at the base of the northern trench is ≥2.5 m,
and episodic thickening of growth strata across these faults into the central structural
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Figure 4.4 Simplified fault trench logs of the southern wall (A) and reversed northern wall (B) of the notrhern
trench, and southern (C) wall of the southern trench show the general structure and stratigraphy of the
trneches. Locations of Figure 4.5A (between meters 7-12 on the southern wall of the northern trench) and
Figure 4.5B (between meters 21-26 on the southern wall of the northern trench) and Figure DR1A (between
meters 7-11 on the northern wall of the northern trench) and Figure DRaB (between meters 21-26 on the
northern wall of the northern trench) are outlined by black corners on logs A and B.

109

Figure 4.5 Detailed photograph logs between meters 7-12 and meters 21-26 from
the southern wall of the northern trench. (A) Photograph log of the main
(eastern)fault strand (visible between meters 7 and 8). Vertical separation is ~1 m
with younger units, 30-50, buttressing against the scarp of unit 70. The vertical
separation, along with fissure fills to the east of the eastern fault strand, provides
evidence for event 3. Upward rupture terminations between meters 9 and 11
provide evidence for the most recent event. (B) Detailed photograph log between
meters 21 and meters 26. The upward rupture terminations may be related to the
penultimate event; however, it is difficult to discern their upward extent, and thus
they may be due to the most recent surface rupture. A fissure fill within unit 70 at
meter 24 provides evidence in support of event 3.
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trough helped us to determine the rupture history of the fault. Both the eastern and
western fault strands are exposed in the northern trench, but only the main, eastern strand
of the fault and the eastern half of the interfault trough are exposed in the southern trench.
Major stratigraphic units are numbered in increments of 10, increasing with depth,
whereas subunits are labeled using a combination of the respective major stratigraphic
unit number plus an alphabetical letter, descending with depth. For example, unit 90 is a
pale yellowish-brown coarse-grained sand and gravel, whereas subunit 90A is a fi ne-
grained layer that makes up the uppermost part of unit 90. Detailed descriptions of the
stratigraphic units are included in Appendix C.

4.5 Age Control
One of the reasons we originally chose the study site was that playas tend to
concentrate charcoal suitable for radiocarbon dating (the low-density charcoal fragments
stay in suspension until deposited with the last remaining water to be evaporated on the
playa). Unfortunately, we were unable to find charcoal in any of the deposits exposed in
the trenches, despite intensive efforts to isolate even small quantities through ―floating‖
the low-density charcoal in settling tubes. Fortunately, however, the sediments at the site
were well suited to optically stimulated luminescence (OSL) dating, which is used to
determine the time that has elapsed since a sediment sample was last exposed to daylight
(Table 4.1) (Aitken, 1998). This technique has been successfully applied to dating
deformed sediments from paleoseismic studies in the western United States (e.g.,
Machette et al., 1992; Crone et al., 1997; Rockwell et al., 2000; Lee et al., 2001; Kent et
111

112

al., 2005; Wesnousky et al., 2005) and elsewhere in the world (e.g., Owen et al., 1999;
Washburn et al., 2001; Wallinga, 2002; Rockwell et al., 2009).
We dated 12 samples using OSL methods. At least two samples were dated from
each of the layers bounding each of the event horizons in order to replicate the ages. The
sediment samples were collected by pounding 5-cm-diameter, 46-cm-long steel pipes
with capped outer ends into the trench wall. The samples remained sealed in their tubes
until processing in the safe-light conditions in the Luminescence Dating Laboratory at
the University of Cincinnati. Sediment from at least 3 cm from both ends of the tube was
removed, and the rest was dried in an oven at ~90 °C. Approximately 20 g of the dried
sediment were ground to a fi ne powder and sent to the U.S. Geological Survey (USGS)
Reactor in Denver for instrumental neutron activation analysis (INAA) to determine the
concentration of radioisotopes for dose-rate determination.
The ages of our samples range from 0.6 ka to 8.4 ka, indicating that deposition of
all of the strata exposed in the trenches occurred during Holocene time (Figure 4.6; Table
4.1). The oldest sample (081407A) was collected from the southern wall of the southern
trench, whereas the rest of our samples came from the southern wall of the northern
trench (Table 4.1). Although the OSL ages indicate that the sediment accumulation rate
has averaged ~0.4 mm/yr over the past 8.4 k.y., the rate has varied significantly over that
time (Figure 4.7). For example, between ca. 5.6 ka and ca. 5.0 ka, the rate of sediment
accumulation increased to ~2 mm/yr, but subsequently decreased to ~0.2 mm/yr between
ca. 5.0 ka and the present.

113

Figure 4.6 Composite stratigraphic column of playa units derived from both
trenches. Black circles are depth locations of dated optically stimulated
luminescence (OSL) samples with the respective ages on the left. Determined
stratigraphic positions of event horizons are also labled on the left. Descriptions of
each unit are provided in Figure 4.4.
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Figure 4.7 Sediment accumulation rate curve showing distribution of optically
stimulated luminescence dates with depth below the surface (measured at meter
21 on the south wall of the northern trench for consistency). Uncertainty
incorporates all random and systematic errors, including dose rate errors and
weighted average uncertainty. The dashed line represents the best estimates of
the sample ages, providing the sediment accumulation rate. The green polygon
represents the error envelpe on the sedimentation rate. Depths of event horizons
are shown at meter 21 from the north wall of the northern trench.
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4.6 Interpretation of Paleo-Surface Ruptures
The trench exposures revealed evidence for four Holocene surface ruptures on the
Calico fault. We refer to these as events 1 (youngest) through 4 (oldest). The three most
recent events are well expressed in the northern trench, whereas evidence for the oldest
event is present only in the southern trench, in which we exposed deeper stratigraphy. As
described in detail next, evidence for these paleoearthquake event horizons includes
fissure fills, the geometry of growth strata (e.g., onlap of fault scarps), and upward fault
terminations.
4.6.1 Event 1
Event 1 is best expressed in the northern trench, where it is recorded by the
geometry of growth strata and upward fault terminations within unit 30, a dense pinkish-
brown clay layer. The best evidence for this surface rupture comes from thickening of
unit 30 into the central trough across both the main (eastern) and western fault zones
(Figure 4.5; Figures C1 and C2). Specifically, unit 30 increases in thickness across the
western fault strand from ~10 cm west of the fault to 30–40 cm in the center of the
northern trench. Unit 30 includes two subunits: unit 30A, denser, more indurated clay,
overlies unit 30B, which is slightly more friable. Unit 30B was most clearly defined on
the southern wall of the northern trench, extending from meter 8, where it is fault contact
with the uplifted older units to the east, across the midtrench trough to the western extent
of the trench.
Unit 30 B exhibits a relatively constant thickness of 10–15 cm, particularly west
of meter 16. In contrast, unit 30A is restricted to the midbasin trough and onlaps unit 30B
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at meter 10 and meter 22 (Figure 4.4). At meter 8, two strands of the main fault offset
subunit 30B, but do not cut overlying unit 10. The eastern of these two strands juxtaposes
unit 30B against unit 70 clay exposed in the uplifted block east of the main fault strand.
Ten centimeters to the west, the second strand exhibits a 10-cm-high, east-side-up
vertical separation of the lower part of subunit 30B.
Unit 30 thins markedly westward at the location of the western fault at meter 21.5.
The exact stratigraphic level of the upward termination of this oblique reverse fault
exposed is not clear; the fault cuts all strata below unit 40, but it cannot be traced
confidently upward through the unit 40 soil overprint or into unit 30. However, the
relatively constant thickness of subunit 30B from meter 16 to the west end of the trench
across this feature argues that subunit 30B was deposited on a near-horizontal surface and
has subsequently been folded by slip on the thrust fault. Subunit 30B is composed of
playa clay, and such fi ne-grained strata can drape significant scarps, but even clay units
would likely exhibit some thickening across such a pronounced topographic scarp if it
had existed prior to deposition of subunit 30B. Taken together, these stratigraphic and
structural observations indicate that the most recent surface rupture at the trench site
occurred after deposition of subunit 30B and before deposition of subunit 30A, which is
interpreted to have largely filled in the post-event structural trough created during event
1.
Thickening of unit 30 into the midtrench trough records sedimentary growth of at
least 20–30 cm following event 1. However, the top of unit 30 adjacent to the western
fault is not flat, suggesting that growth of unit 30A did not completely fill the trough to
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its pre-event, horizontal playa surface, leaving a subtle (~10 cm high on southern wall,
~30 cm high on northern wall) east-facing scarp. This remaining subtle event 1 scarp was
subsequently completely buried during deposition of unit 10, which extends up to the
current near-horizontal playa surface. Thus, total vertical separation in event 1 across
both strands is probably at least ~30 cm, and possibly more than 60 cm.
OSL sample 081507A from subunit 30B and samples 051707J and 051707B from
subunit 30A constrain the age of event 1. The lower sample yielded an age of 2.0 ± 0.1
ka, whereas the upper samples yielded ages of 0.6 ± 0.1 ka and 1.1 ± 0.1 ka, respectively.
Thus, the most recent surface rupture at the trench site occurred after 2.0 ± 0.1 and before
0.6 ± 0.1 (or 1.1 ± 0.1) ka. We note, however, that if there was any undetected partial
bleaching of these (very young) samples, this would result in ages that are slightly too
old. Whereas the general reproducibility of the ages of the other sample pairs from deeper
in the section argues that partial bleaching is not a major problem in the trench, the ~500
yr difference in the ages of samples 051707J and 051707B, which were collected from
the same stratigraphic level only 30 cm from each other, suggests that there may be some
mi nor partial bleaching in some samples. Although we suspect that this effect is
relatively minor, it would be most pronounced in the youngest samples. Thus, the OSL
ages constraining event 1 should probably be considered maxima.
The upward terminations of the secondary fault strands exposed at meter 9.5 and
meter 11 require additional discussion. Both of these faults clearly extend upward to at
least the top of unit 40, but they cannot be traced confidently upward into unit 30B. We
suspect that this is because the shallowest few tens of centimeters of the trench exposures
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encompassing units 10–30 exhibited pervasive, irregular cracking. This cracking does not
appear to be tectonic in origin, but rather is related to development of a weak, blocky soil
texture in these units. Thus, although the stratigraphic contacts in this section could be
mapped in detail, the exact upward terminations of the faults could not be unequivocally
distinguished from nontectonic cracking within the lower part of unit 30. The possibility
that the faults at meter 9.5 and meter 11 do terminate upward at the base of unit 30B
suggests the possibility of another event horizon at this stratigraphic level.
If these upward fault terminations do record an additional, pre–event 1 surface
rupture, this event must have occurred before deposition of unit 30B at 2.0 ka, and after
the 3.4 ka age of unit 40. The 3.4 ka OSL date from unit 40, however, dates the
deposition of this unit, and these sediments must have been exposed at the ground surface
for a significant period of time prior to deposition of subunit 30B, as evidenced by the
presence of the cambic and carbonate soils that developed within unit 40, but which are
not evident in unit 30. The observation that the faults at meter 9.5 and meter 11 are
clearly discernible to the top of unit 40, through the cambic and carbonate soil overprints,
indicates that these faults must have ruptured after most, or all, pedogenesis in unit 40.
Thus, if the poorly defined upward terminations of these faults do record a distinct event
horizon, this earthquake must have occurred just before deposition of unit 30B at ca. 2 ka.
Evidence against the occurrence of a separate event horizon at the base of unit 30B
includes: (1) the inconclusive stratigraphic level of the upward terminations of these
faults, which may have been obscured by pervasive soil-related cracking of unit 30; and
(2) the complete absence of any stratigraphic or structural evidence for significant
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vertical separations of the unit 40–subunit 30B contact across the faults at meter 9.5 and
meter 11.This is in marked contrast to the four surface ruptures that we documented, all
of which exhibit significant vertical separations. Moreover, subunit 30B consists of clay
that was deposited in a low-energy playa environment, thus making it unlikely that post–
unit 40 erosion beveled off any scarps associated with the meter 9.5 and meter 11 faults
strands. It is more likely, in our view, that these faults exhibited only minor slip in the
most recent event, and are present, but difficult to discern within subunit 30B.
Alternatively, many small-displacement faults may not reach all the way to the surface in
earthquakes (e.g., Bonilla and Lienkaemper, 1990). Thus, although it is possible that
another surface rupture occurred just before event 1, prior to deposition of unit 30B, we
think this possibility is unlikely.
Weak evidence for a possible post–event 1 surface rupture comes from east of the
main fault, where at least six cracks and small fissures terminate ~0.1–0.2 m below the
present ground surface at the base of, or within, unit 20, to the east of the main fault at
meter 8 on the southern wall of the northern trench. Unit 20 is lithologically similar to
unit 30, and these units may be correlative. However, unit 20 is only exposed on the
eastern side of the eastern fault in our northern trench, so this correlation remains
somewhat speculative, and the implication of these cracks (which do not appear to have
accommodated any slip) remains unclear. If these cracks are younger than event 1, it is
possible that they record cracking of the playa surface during strong ground shaking in
other earthquakes (i.e., they did not record actual surface rupture on the Calico fault at
our trench site).
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4.6.2 Event 2
The penultimate surface rupture (event 2) is defined in the northern trench by both
upward fault terminations and sedimentary growth of units 40 and 50 across both the
eastern and western fault strands into the central trough. As described in detail in the
stratigraphic section of the Data Repository material (see footnote 1), units 40 and 50 are
the same depositional unit. We distinguish unit 40 as a separate unit based on the
development of a weak cambic soil that has been overprinted by a stage II carbonate soil.
The depositional unit made up of units 40 and 50 consists predominantly of lacustrine,
medium- to coarse-grained sand along with several pale-brown clay subunits that are
continuous throughout the northern trench. Within unit 50, the presence of several thin,
laterally continuous clay layers allows us to define the geometry of sedimentary growth
following event 2, as well as the exact stratigraphic position of the event horizon. Unit
40/50, which onlaps eastward against the fault scarp of event 3 (discussed in the
following section), thickens eastward across the western fault strand from a thickness of
~20 cm at meter 26 to a thickness of ~120 cm at meter 12. The parallelism of the
lowermost clay subunits within unit 50 suggests that they were deposited on a relatively
horizontal substrate. In contrast, fanning of bedding dips for the overlying clay interbeds
at meter 10.5–12.0 records onlap during sedimentary growth above a west-facing scarp
that developed along the main (eastern) fault during event 2 (Figure 4.5). The geometry
of these growth strata indicates that the event horizon for the penultimate surface rupture
lies near the middle of unit 50. This observation is supported by minor reverse faulting
that occurred during event 2 between meters 21 and 22 along the secondary, western fault
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strand (Figure 4.5; Figure C1). This strand displaces the layers below unit 50, as well as
the lowest subunits within it, and terminates upward within the upper half of unit 50.
Additional evidence in support of event 2 is provided by an upward fault termination at
an interbedded clay subunit of unit 50 near meter 24.5 on the southern wall of the
northern trench.
Thickening of unit 50 (from a thickness of 20 cm to a thickness of 120 cm) from
meter 26 to meter 12 in the section of the midtrench trough records sedimentary growth
of at least 1.0 m following event 2. This stratigraphic growth can be interpreted as a
minimum because unit 50 is not exposed east of the main fault at meter 8, and therefore
the upper part of unit 50 may have been eroded. Thus, the total vertical separation in
event 2 is likely on the order of ~1.0 m.
We dated one sample (081507H) from the bottom of unit 50 and two samples
(081507G and 081507F) from the top of the unit, bracketing the occurrence of event 2.
The lower sample yielded an age of 5.6 ± 0.4 ka, whereas the upper samples yielded an
age of 5.0 ± 0.4 ka. These OSL dates indicate that event 2 occurred between 5.6 ± 0.4 ka
and 5.0 ± 0.4 ka.
4.6.3 Event 3
Event 3 is well expressed in the northern trench, where it is defined by the
geometry of growth strata, upward fault terminations, and multiple fissure fills within
unit 70, a pinkish-brown clay (Figure 4.5; Figures C1 and C2). The sedimentary growth
during event 3 is most pronounced across the main (eastern) fault zone, where unit 70
thickens westward from ~50 cm at meters 8–11 to >1 m west of meter 11. East of meter
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8, unit 70 thins and pinches out eastward by meter 3. The pronounced difference in
thickness (0.6 m) of unit 70 between meter 7.5 (east of the main fault) and meter 8.5
(west of the fault) probably reflects erosion of the top of the layer east of the fault.
Alternatively, it may reflect strike-slip juxtaposition of a layer of variable along-strike
thickness. We think this is less likely, however, because of the near-horizontal
morphology of the site, as reflected in the highly planar nature of most of the strata
expressed in our trenches. Significant erosion of unit 70 east of the fault is also indicated
by the fact that it is overlain directly by the much-younger unit 20. We did not fully
expose the unit 70-80 contact across the entire length of the down-dropped, midtrench
trough, but unit 70 thins westward from at least 90 cm at its thickest point adjacent to the
main (eastern) fault to ~60 cm west of meter 22 across the western fault strand.
Based on the geometry of several fissure fills and the depth of upward fault
terminations, event horizon 3 lies within unit 70. Specifically, the event horizon is
marked by the top of a fissure fill at meter 24. The fissure extends downward for ~70 cm
through unit 80 and is filled with clay from unit 70. Moreover, we were able to trace a
weakly developed paleosurface for several meters to the east and west of the fissure on
the southern wall of the trench at the same stratigraphic level as the fissure fill. A similar
fissure fill was observed in the northern wall of the northern trench at meter 10 at the
same stratigraphic level (Figure C1). Moreover, the occurrence between meter 8 and
meter 3 of multiple fissures within units 80C, 80D, 90, and 100 filled with clay from the
lower part of unit 70 suggests that the lower part of unit 70 was at the ground surface
during event 3. A fault between meter 11 and meter 12 also terminates upward at the
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same stratigraphic level as the top of the fissure fill. Unit 70 does not thicken appreciably
across the western fault zone, implying that this fault strand experienced minor slip
during event 3.
Two OSL samples (081507E and 081507D) from the bottom of unit 70 and two
(081507C and 081507B) from the top of the unit constrain the age of event 3. The lower
samples yielded ages of 6.1 ± 0.4 ka and 7.3 ± 0.5 ka, whereas the upper samples yielded
ages of 5.4 ± 0.4 ka and 5.6 ± 0.4 ka. These ages indicate that event 3 occurred before 5.4
± 0.4 ka (or 5.6 ± 0.4 ka) and probably after 6.1 ± 0.4 ka. We suspect that the 7.3 ± 0.5 ka
age, which was collected from the same stratigraphic level as the 6.1 ± 0.4 ka age, may
be less reliable because this sample exhibited the lowest dose rate of all the samples
dated, perhaps resulting in an anomalously old age. Alternatively, if the 7.3 ± 0.5 ka age
is valid, then event 3 occurred between 5.4 ± 0.4 ka and 7.3 ± 0.5 ka.
4.6.4 Event 4
Event 4, the oldest event horizon we describe, was only observed in the southern
trench, where slightly slower sediment accumulation rates allowed us to expose deeper
stratigraphic levels (Figure 4.4C; Figure C2). The event is defined by geometry of growth
strata and upward fault terminations. Specifically, if we assume that unit 70, which
contains the event 3 horizon in the northern trench, was located near the present ground
surface to the east of the main strand in the southern trench (i.e., above unit 90 on the east
side of the fault), as seems likely, then the total event 4 vertical separation is ~1.5 m
across the main strand between meter 3 and meter 4 in the southern trench. The large
minimum vertical separation across the top of unit 90 suggests that event 4 was a
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relatively large-displacement event. Event 4 is also defined by two fault strands that
terminate upward within unit 80D (at meter 3 and meter 4). Moreover, unit 80D, which
developed above unit 90, thins eastward against a preexisting scarp that ruptured the top
of unit 90 or the lower part of unit 80D. We interpret this as possible evidence for an
older event, although this scarp could also have formed during event 4. The overlying
unit 80C pinches out against the west-facing scarp formed during event 4. Unit 80A does
not change thickness within the trench exposure west of the fault, suggesting that post–
event 4 deposition of unit 80C and the upper part of unit 80D had filled in the down-
dropped area to the west of the fault and reestablished a near-horizontal surface. These
observations indicate the occurrence of at least one surface rupture (i.e., event 4) either
during or immediately after the latter stages of deposition of unit 80D.
One OSL sample (081407A) from the top of unit 90 in the southern trench, and
two samples (081507E and 081507D) from the bottom of unit70 in the northern trench,
bracket the age of event 4. The sample from unit 90 yielded an age of 8.4 ± 0.7 ka,
whereas the two unit 70 samples yielded ages of 6.1 ± 0.4 ka and 7.3 ± 0.5 ka. These
three ages indicate that event 4 occurred before 6.1 ± 0.4 ka (or less likely 7.3 ± 0.5 ka)
and after 8.4 ± 0.7 ka. As explained earlier, we suspect that the 7.3 ± 0.5 ka date may be
less reliable than the 6.1 ± 0.4 ka date because the older sample exhibited the lowest dose
rate of all the samples we dated.

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4.7 Measurement of Small-Scale Geomorphic Offsets
In addition to our trench study, we also measured displacements in Holocene
alluvial deposits exposed over an 8 km length of the fault extending southward from the
trench site. We focused on small-scale displacements (<10 m) in an effort to define slip
during the past several surface ruptures of most relevance to our paleoseismologic results.
Measured displacements at 16 different locations include horizontal and vertical offsets
of channels and alluvial-fan surfaces that range from 1.1 ± 0.2 m to 8.7 +2.3/–4.1 m
(Figure 4.8; Table 4.2). Several of these offsets are preserved along a releasing bend of
the Calico fault. In some cases, only one (horizontal or vertical) component of oblique
slip could be measured, and total offset was inferred from the ratio of horizontal to
vertical displacements at nearby sites (Figure 4.8). Altogether the measured
displacements fall into two sets: one set of six, ranging from 4.6 ± 0.7 m to 8.7 +2.3/–4.1
m, with an average of 6.7 ± 3.0 m, and a second set of 10, ranging from 1.1 ± 0.2 m to 3.0
± 1.0 m, with an average of 2.0 ± 1.0 m. The presence of at least two different sets of
displacements is further implied by the total oblique displacement of 2.1 ± 0.7 m at
location 14 and 4.5 ± 0.7 m at location 13 (Figure 4.8; Table 4.2). At these adjacent
locations, a fault scarp (location 14) is present in an offset channel inset into a displaced
alluvial fan (location 13). This observation suggests that the channel was incised after at
least one earthquake that offset the alluvial-fan surface, and that a subsequent earthquake
offset the channel further.
Although it is possible that multiple earthquake events are represented within each set of
displacements, we did not observe evidence for more than two events in the field. We
126

prefer an interpretation of two to three events, where the set of smaller- displacement
measurements (1.1–3.0 m) records slip in a single earthquake, despite the variability of
these offsets (~1 to ~3 m). Given the overlapping distribution of measurement errors of
the smallest set of offsets, this interpretation seems likely, and such along-strike
variations in slip at adjacent sites have been noted in surface ruptures on other faults (e.g.,
McGill and Rubin, 1994).
If we account for an average of 2.0 ± 1.0 m of displacement during the most
recent event, the penultimate event had an average slip of ~4.7 ± 2.0 m. Alternatively, the
average displacement of 4.7 ± 2.0 m may record slip from two different surface ruptures
(events 2 and 3), which our paleoseismic data indicate happened closely spaced in time.
The potentially brief inter-event time between events 2 and 3 suggests that new
geomorphic features (e.g., gullies) may not have had sufficient time to develop between
these earthquakes. In such a situation, the offsets in events 2 and 3 would appear as a
single geomorphically defined offset. In summary, we interpret the two sets of
displacements (2.0 ± 1.0 m and 6.7 ± 3.0 m) to record the most recent two, and possibly
three, surface ruptures on the Calico fault south of Newberry Springs. However, because
we lack age control for the features that are offset, these displacements should be
considered maxima for the most recent two (and likely three) events revealed by our
trenching study.

127

Figure 4.8 (A) Map showing a part of the northern Calico fault extending
southward from our trench site (white star). Circles show the locations of the
measured horizontal offsets identified along the fault. The solid black squares are
locations along a releasing bend of the fault with observed oblique-normal motion.
The white squares are locations along the fault where the oblique component of the
fault was calculated knowing either the normal or dextral component and
assuming a ration from an adjacent site. (B) Graph showing measured dextral and
oblique displacements along the fault. See Table 4.2 for details.
128

129

4.8 Discussion
The paleoseismologic data described here demonstrate that the Calico fault has
ruptured to the surface at least four times over the past ~9 k.y. (Figure 4.9). The ages of
these surface ruptures strongly support the hypothesis that earthquake recurrence in the
Mojave section of the Eastern California shear zone is temporally clustered, as originally
proposed by Rockwell et al. (2000). Specifically, the most recent event on the Calico
fault occurred after 2 ka, as part of an ongoing cluster of earthquakes in the Eastern
California shear zone that has been occurring over the past ~1000–1500 yr. Moreover, we
see no evidence for any Calico fault surface ruptures during the pronounced seismic lull
documented by Rockwell et al. (2000) between 2 and 5 ka, despite the continuous, well-
dated stratigraphy exposed in our trenches for this time interval. The penultimate and
antepenultimate events on the Calico fault, at 5.0–5.6 ka and 5.6–6.1(or 5.6–7.3 ka),
respectively, also occurred during a pronounced cluster at 5–6 ka documented for other
faults in the Mojave part of the Eastern California shear zone by Rockwell et al. (2000).
Thus, the Calico fault ruptured twice during the penultimate Eastern California shear
zone cluster. Finally, although the timing of the antepenultimate cluster documented by
Rockwell et al. (2000) is only broadly constrained between ca. 7 and 11 ka, with a peak
in moment release at ca. 8–9.5 ka, it appears that our event 4 occurred toward the end of
the cluster between 7.3 ± 0.5 and 8.4± 0.7 (or 6.1 ± 0.4 and 8.4 ± 0.7) ka (Figure 4.9).
Evidence for two surface ruptures between 5 ka and 6 ka indicates that the Calico
fault can rupture more than once during each cluster. Thus, although the occurrence of
130

Figure 4.9 Composition of our paleoearthquake ages (black bars) and compilation
of seismic moment release data in the Eastern California shear zone through time
(blue) from Rockwell et al. (2000). Not the close correspondence of the event ages on
the Calico fault (this study) with periods of increased seismic moment release in the
region. Circled numbers indicate the four events identified in this study.
131

the most recent event after 2 ka suggests that the Calico fault has already ruptured as part
of the latest, ongoing earthquake cluster in the Eastern California shear zone, the fault
may still be at risk of a near-future earthquake. Furthermore, because no paleoseismic
evidence exists for a surface rupture in the past ~600 yr, it is unlikely that the Calico fault
ruptured in 1887, as suggested by Bakun (2005). One explanation for these temporally
close ruptures is that this section of the fault was an overlap zone between two ruptures
on the southern and northern parts of the Calico fault system. Another possibility is that
during the 5–6 ka seismic cluster, strain was released in two events on the Calico fault. At
this time, we lack sufficient slip-per-event data to test these alternative rupture scenarios.
However, the slip-per-event data gathered thus far suggest that ruptures of the Calico
fault are similar in size to earthquakes on nearby shear-zone faults (~3 m per earthquake;
Rockwell et al., 2000). A higher earthquake frequency thus seems necessary to account
for the higher slip rate of the Calico fault when compared to other nearby dextral faults in
the Eastern California shear zone.
The vertical separations measured in the paleoseismic trenches may provide some
insight into the displacements that occurred during the three most recent earthquakes on
the Calico fault. If we assume that the slip vector has remained constant at our study site
over the past three events, then the vertical components of the total offsets in each event
reflect the relative size of each slip event. The most recent event shows a vertical
separation of 0.5 m, suggestive of a small overall displacement. In contrast, the
penultimate and antepenultimate surface ruptures exhibit larger vertical separations of ~1
m each, consistent with larger overall displacement in each event. The small vertical
132

separation during the most recent event observed in the trench is consistent with small
(~2.0 ± 1.0 m) displacements measured from nearby geomorphic offsets. The remaining
geomorphically measured slip (4.7 ± 2.0 m) may be attributed to either one larger
penultimate event, consistent with the larger vertical displacement observed in the trench,
or it may represent the penultimate and antepenultimate events, which would imply a
similar average slip of 2–3 m in each event. Geomorphic offsets on the order of ~2–4 m
along the Calico fault imply earthquakes ranging from Mw 7.0 to 7.3 (e.g., Wells and
Coppersmith, 1994). The occurrence of larger-displacement events 2 and 3 of the
penultimate cluster raises the possibility that the apparently small displacement during
the most recent event may be indicative of an ongoing slip deficit.
Interestingly, in addition to the current seismic cluster, the Eastern California
shear zone appears to be experiencing a strain transient characterized by geodetic rates
(100–101 yr) that are faster than the long-term geologic rates (100–106 yr) (Peltzer et al.,
2001; Oskin and Iriondo, 2004; Dolan et al., 2007; Oskin et al., 2008). Oskin et al. (2008)
documented a cumulative slip rate across the Eastern California shear zone at 35°N of
≤6.2 ± 1.9 mm/yr. In contrast, the rate of right-lateral shear across the entire Mojave
Eastern California shear zone measured by global positioning system (GPS) geodesy is
10–14 mm/yr (Savage et al., 1990; Sauber et al., 1994; Dixon et al., 1995; Gan et al.,
2000). Thus, there appears to be a significant discrepancy between the short-term rate of
elastic strain accumulation measured geodetically and the longer-term geologic slip rates.
These observations suggest that the aseismically deforming lower crust and upper mantle
beneath the Eastern California shear zone are shearing at a rate that is faster than the
133

long-term average rate documented geologically. Mechanically, this implies that an
elevated shear strain rate, likely on a localized, transiently weakened ductile shear zone
or set of shear zones, is driving the current cluster of major earthquake activity here
(Peltzer et al., 2001; Oskin and Iriondo, 2004; Dolan et al., 2007; Oskin et al., 2008).
The mechanisms that permit variable loading rate, and the feedback relationships that
may exist among shear-zone strength, fault loading, and earthquake activity, remain
unresolved (Montesí and Hirth, 2003; Dolan et al., 2007; Oskin et al., 2008).
Regardless of the exact mechanism that controls the regional clustering of
earthquake activity, or whether or not there is a correlation between earthquake clusters
and transiently elevated rates of elastic strain accumulation, the paleoseismologic data
from the Calico fault trenches strongly support the notion that seismic moment release
within the Eastern California shear zone is highly episodic. Similar examples of spatially
and/or temporally clustered seismic moment release have been observed elsewhere on
both single faults (e.g., Marco et al., 1996; Stein et al., 1997; Hartleb et al., 2003, 2006;
Friedrich et al., 2003; Rockwell et al., 2009b) and regional fault networks (e.g., Dolan
and Wald, 1998; Rockwell et al., 2000; Dolan et al., 2007). These observations have
fundamentally important implications for probabilistic seismic hazard analysis.
Specifically, the increasing body of evidence for clustered earthquake occurrence for at
least some, and perhaps many, faults and fault systems (including, for example, the
Calico fault) suggests that seismic hazard may be strongly affected by temporally and
spatially clustered moment release over epochs much longer than the typical decadal time
scale of postseismic relaxation.
134

4.9 Conclusions
Paleoseismic trenches demonstrate that the past four surface ruptures on the
Calico fault (event 1, 0.6 [or 1.1 ka] to 2.0 ka; event 2, 5.0 ka to 5.6 ka; event 3, 5.6 to 6.1
ka (or 7.3 ka); event 4, 6.1 to 7.3 ka [or 8.4 ka]) occurred during clusters of seismic
moment release identified earlier on other faults in the Eastern California shear zone as
documented by Rockwell et al. (2000). Two different sets of geomorphic displacements
(2.0 ± 1.0 m and 4.7 ± 2.0 m) measured in the 8 km south of the trench site suggest that
the past two (or three) of the Calico fault earthquakes were large-magnitude (Mw = 7.0–
7.3) events similar in size to the 1992 Mw 7.3 Landers and 1999 Mw 7.1 Hector Mine
earthquakes. Although the most recent event we documented in the trenches occurred
after ca. 2 ka, during the ongoing Eastern California shear zone seismic cluster, evidence
for two Calico fault surface ruptures during the 5–6 ka cluster suggests the possibility that
the Calico fault may rupture more than once during each clustering time period. The
evidence of seismic clustering on a regional network of faults provided in this paper adds
to a growing body of data suggesting that episodic moment release is common on many
faults and fault systems, possibly in response to enhanced loading. Future probabilistic
hazard analyses need to account for the possibility of temporally and spatially clustered
seismic moment release.

135

CHAPTER 5:
Conclusions

5.1 Summary
I have utilized the latest analytical and dating techniques, such as high-resolution
light detection and ranging (LiDAR) data, terrestrial cosmogenic nuclide (TCN)
geochronology, and optically stimulated luminescence (OSL) dating, to quantify the slip
rates and determine the ages of past earthquakes over Pleistocene-Holocene timescales
along the Fish Lake Valley fault (FLVF), Garlock fault, and Calico fault in the Eastern
California shear zone (ECSZ). The results that I have obtained as part of my Ph.D.
research have allowed us to better understand (1) strain accumulation and release
patterns, as well as (2) seismic clustering in the ECSZ and consequently the Pacific-North
America plate boundary. A summary of these results, presented in detail in the previous
three chapters, is provided below.

5.2 Constancy of Seismic Strain Release
I studied the constancy of strain release along two major fault systems in eastern
California: (1) the Fish Lake Valley fault; and (2) the Garlock fault. The detailed analyses
and results are described in chapters 2 and 3, respectively.
5.2.1 Constancy of Seismic Strain Release in the Northern Eastern California Shear
Zone
Through the integration of LiDAR topographic data and
10
Be TCN
geochronology, I was able to determine the extension rates along the fastest slipping
fault, i.e., Fish Lake Valley fault, in the northern ECSZ. This research project followed a
136

previous study on the FLVF done by Frankel et al., (2007b) where the strike-slip slip
rates were determined using the same analytical approach. The extension displacements,
assuming an average dip angle of 60°, resolved at N65°E at four different locations are
12.4 ± 0.6 m (5% error bars), 41.2 ± 2.1 m, 49.0 ± 2.5 m, and 37.0 ± 1.9 m, from south to
north respectively. The combination of these displacements with ages of the displaced
surfaces determined by cosmogenic
10
Be geochronology yields late Pleistocene extension
rates of 0.1 ± 0.1 mm/yr, 0.3 ± 0.2 mm/yr, 0.7 +0.3/-0.1 mm/yr, and 0.5 +0.2/-0.1 mm/yr,
from south to north respectively.
Combining these rates with the extension rates of the rest of the faults in the
northern ECSZ, such as the White Mountains fault (Kirby et al., 2006), distributed
normal faulting in the Volcanic Tablelands (Sheehan, 2007), and the Sierra Nevada
frontal fault (Le et al., 2006), including the Round Valley and Hilton Creek faults north
of Owens Valley (Berry, 1997) imply that the long-term geologic extension rate is similar
to the short-term geodetically determined extension rate across the northernmost ECSZ,
both of which are ~1 mm/yr. This comparison suggests that the rate of extension at the
latitude of northern Fish Lake Valley may have remained relatively constant over the past
10
4
– 10
5
yr, although it is also possible that temporal variations in slip rate have occurred
over shorter time scales on the various faults that accommodate extension across the
region. Additional slip rate calculations on all of these faults at a wider span of time
scales are necessary to test whether such temporal variations in rate have occurred.

137

5.2.2 Constancy of Seismic Strain Release on the Garlock Fault
Through my analysis on the Garlock fault, I was able to determine a latest
Pleistocene-early Holocene slip rate of 5.3 +1.0/-2.0 mm/yr, and a possible maximum
rate based on the offset of a deeply incised channel thalweg of ~6.6 ± 1.2 mm/yr. Such a
geologic slip rate is in general agreement with most previously determined longer-term
(Miocene-age) geologic slip-rates. For example, early Miocene volcanic and sedimentary
rocks that are sinistrally offset ~64-km suggest a minimum slip rate of ~3.8 mm/yr since
the time of fault initiation (Monastero et al., 1997). Similarly, Carter et al. (1994)
determined a slip rate of 5.5-8 mm/yr based on the offset Bedrock Springs Formation,
while Burbank and Whistler (1987) and Loomis and Burbank (1988) suggested a
Miocene slip rate of 6-9 mm/yr.
In comparison, late Pleistocene-early Holocene slip rates, including this study,
range from 4-9 mm/yr with a preferred slip rate of 5-7 mm/yr (Clark and Lajoie, 1974;
McGill, 1992; McGill and Sieh, 1993; McGill et al., 2009; this study). These slip rates
which come from various locations, i.e., from the eastern end of the western Garlock fault
(e.g., McGill et al., 2009), the central Garlock fault (Clarck and Lajoie, 1974; this study),
and the western end of the eastern Garlock fault (e.g., McGill, 1992; McGill and Sieh,
1993), show a consistent slip rate through the straight, less-structurally complicated,
central Garlock fault section over the past ~10,000 years.
However, geodetic measurement studies of strain accumulation on the Garlock
fault have continuously indicated sinistral slip rates that are significantly lower than
geologically determined slip rates. Such slower geodetically derived slip rates measured
138

along the central section of the fault, suggest that the Garlock fault is currently
experiencing a period of transient strain accumulation, in which the lower curst (and
mantle?) beneath the fault is deforming at a rate that is much slower than its long-term
average rate. These observations suggest that the Garlock fault possibly experiences two
modes of strain accumulation; the current ―slow‖ mode, in which strain accumulates very
slowly along the fault, and ―fast‖ modes, during which the fault must store elastic strain
energy at much faster rates than the long-term average in order to account for the
relatively rapid geologic slip rates measured along the central part of the fault.

5.3 Spatial Variations in Slip Rate along the Fish Lake Valley Fault
Based on the results from my research, variations in slip rates occur along the
Fish Lake Valley fault, where the extension rates increase northward from 0.1 ± 0.1
mm/yr to 0.5 +0.2/-0.1 mm/yr in the northernmost part of the fault. In comparison,
Frankel et al. (2007b) documented a northward strike-slip rate decrease from 3.5 mm/yr
to 2.5 mm/yr. The northward increase in extension rate and the northward decrease in
dextral slip rate reflect transfer of slip off the predominantly right-lateral FLVF and onto
north- and northeast-trending normal faults as part of a distributed zone of slip transfer
located in the ~40-km-long by 30-km-wide, triangular area east of the Fish Lake Valley
fault between the Emigrant Peak fault and the east-trending left-lateral faults of the Mina
Deflection. In other words, the change in slip motion is due to the strain transfer from the
faults of the ECSZ onto the east-west oriented Mina Deflection zone, and onto the
Walker Lane belt further north. These observations have important implications for the
139

distribution of strain along this section of the Pacific-North America plate boundary, and
more generally for mechanisms of slip transfer along evolving, structurally complex fault
systems.

5.4 Seismic Clustering in the Southern Eastern California Shear Zone
I studied the potential of seismic clustering along the Calico fault, the fastest-
slipping fault in the southern ECSZ. Through the combination of paleoseismic
investigation and OSL geochronology I was able to determine the occurrence of four past
surface ruptures: event 1- 0.6 ka to 2.0 ka; event 2- 5.0 ka to 5.6 ka; event 3- 5.6 ka to 6.1
(or 7.3 ka); and, event 4- 6.1 (or 7.3 ka) to 8.4 ka.
These results suggest that the earthquakes on the Calico fault occurred during
clusters of increased seismic moment release identified earlier on other faults in the
Eastern California shear zone as documented by Rockwell et al. (2000). In addition, two
different sets of geomorphic displacements (2.0 ± 1.0 m and 4.7 ± 2.0 m) measured along
the fault ~8 km south of the trench site suggest that the past two (or three) earthquakes on
the Calico fault were similar in magnitude to the 1992 M
w
7.3 Landers and 1999 M
w
7.1
Hector Mine earthquakes. The evidence of seismic clustering on a regional network of
faults provided in this dissertation adds to a growing body of data suggesting that
episodic moment release is common on many faults and fault systems. Therefore, future
probabilistic hazard analyses need to account for the possibility of temporally and
spatially clustered seismic moment release.

140

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160

APPENDIX A:
Fish Lake Valley Fault Scarp Profiles and Displacement Measurements

The figures (Figures A-1 and A-2) and Table A1 on the following pages
correspond to the fault displacement data presented in Chapter 2. These figures and table
provide a comprehensive view of the analysis undertaken in order to determine the
average displacements at the four sites along the Fish Lake Valley fault.

161

Figure A1 Complete list of the analyzed topographic profiles across alluvial fan
surfaces and calculated vertical components of displacement from the four study
sites: (A) Indian Creek; (B) Perry Aiken Creek; (C) Wildhorse Creek; (D)
Furnace Creek. See Figures 2.4-2.7 for locations of the profiles.
162

Figure A-1: Continued
163

Figure A1: Continued
164

Figure A1: Continued
165

Figure A1: Continued
166

Figure A1: Continued
167

Figure A2 Restoration of right lateral offset at Perry Aiken. Restoration of the
offset walls of the southern channel is highlighted in blue.
168

169

Table A1: Continued
170

Table A1: Continued
171

APPENDIX B:
Paleoseismologic Trenching and Geochronology of the Calico Fault

B1 Paleoseismologic Trenching
We used a standard backhoe to excavate the trenches. Aluminum hydraulic shores
were emplaced to ensure trench safety, and the walls were carefully scraped and cleaned
to remove any smear created by the backhoe bucket. String lattices were strung on both
walls of the northern trench and the southern wall of the southern trench creating grids
that were 100 cm (horizontal) by 50 cm (vertical). The trench walls were logged at a
scale of 1:15. Locations of sedimentary units, and sediment and tectonic structures were
recorded and reported hereinafter according to their trench coordinates, using a horizontal
meter measurement staring from the east end of the trenches, and a vertical meter
measurement staring from an arbitrary ―0‖ datum. Each grid was logged manually and
digitally photographed using a wide-angle camera lens. At a later stage, all photographs
were corrected for distortion caused by the camera lens, and also brightness adjustments
were made due to lower sun-exposure of the grids at the bottom of the two trenches. All
corrected images were finally merged into a photomosaic collage and detailed logs were
drafted (Fig. DR3).
Both trenches provide exposure of the main fault zone where units are separated
vertically as much as ~0.7 m in the northern trench and ~1.5 m in the southern trench.
Evidence for the three most recent events comes from the northern trench, while the
oldest event in our study is exposed only in the deeper southern trench. Major
stratigraphic units are numbered in increments of 10, increasing with depth, whereas sub-
172

units are labeled using a combination of the respective major stratigraphic unit number
plus an alphabetical letter, descending with depth. The oldest unit (unit 100) that we
observed is a very-fine-grained, dense green clay that is exposed only at the base of the
section to the east of the eastern (main) fault strand. Overlying this is a 1-m-thick layer,
unit 90, composed of coarse-grained sand and gravel that ranges in color from light
yellowish-brown to red (locally pale green), and that is locally coated with black
manganese oxide. These gravels display both horizontal stratification and prominent
cross-stratification, and we interpret the unit to have been deposited in a shallow
lacustrine environment. This is the layer with the oldest OSL age that we obtained –
8.4±0.7 ka. Unit 90 is capped by a fine-grained layer which we label as 90A. Above the
coarse-grained sands lie well-sorted light greenish-gray sediments. Based on grain size
(clay to pebbles), unit 80 can be divided into at least four distinct sub-units (80A, 80B,
80C, and 80D), although the boundaries between them are generally gradational over 5-
10 cm. The next-youngest unit is a thick, very pale brown clay layer (unit 70), which is 1
m thick in the northern trench. Unit 70 is one of the thickest layers in the northern trench,
but is almost nonexistent in the southern trench. The bottom of this unit yields OSL ages
of 6.1±0.4 and 7.3±0.5 ka (two samples dated), whereas the top has OSL ages of 5.4±0.4
and 5.6±0.4 ka (two samples dated). Directly above unit 70 is a darker pinkish-brown
layer (unit 60), which is only ~0.15-0.20 thick. It appears to be separated from the paler
clay below by flame structures, suggesting liquefaction of water-saturated sediments
(probably related to Event 2- see main text for discussion of that surface rupture). On top
of this unit is a series of interbedded very pale brown, medium-grained sands, fine-
173

grained sands, and clays (unit 50), roughly 0.75 m thick in the northern trench but only
0.30 cm in the southern trench. This layer consists of at least three subunits labeled 50A,
50B, and 50C. The bottom of unit 50 has an age of 5.6±0.4 ka, whereas the top yields an
age of 5.0±0.4 ka (two samples dated). Above this is a carbonate-rich clay layer (unit 40),
light brown in color, which we interpret as a cambic soil horizon with an age of 3.4±0.2
ka. Depositionally, unit 40 is part of unit 50. However, we distinguish it as a separate unit
based on the development of a carbonate soil overprinted by a cambic soil. Clays and
fine-grained sands lie above unit 40, likely the result of playa deposition in late Holocene
time.
On the western side of the fault, the oldest of these layers is a very fine-grained,
pinkish-brown clay (unit 30) with distinct upper and lower boundaries. This clay is
generally ~0.1 m thick, but it almost doubles in thickness in the footwall of a reverse fault
14 m west of the main strand of the Calico fault. A narrow (~5 cm) lens of very fine-
grained sand of the same color is interbedded within this clay layer. One OSL sample was
dated from the bottom (2.0±0.1 ka) and two from the top (1.1±0.1 and 0.6±0.1 ka) of unit
30. The clay does not appear on the eastern side of the main fault strand, but a friable,
pinkish-brown, very fine-grained sand layer (unit 20) does; this 5-cm-thick fine-grained
sand does not exist on the western side of the fault. Both, the clay on the western side and
the sand on the eastern side of the fault pinch out within 0.25 m of the main fault. The
top-most stratigraphic unit (unit 10) is the most recently deposited playa sediment: a very
fine-grained, pinkish-gray silt (~0.3 m). This massive uppermost unit is unbroken by the
174

most recent surface rupture, although it exhibits a substantial (~0.25 m) change in
thickness across the fault, thinning to just 5 cm on the east side of the main fault strand.

B2 Optically Stimulated Luminescence (OSL) Geochronology
The OSL technique relies on the interaction of ionizing radiation with electrons
within semi-conducting minerals resulting in the accumulation of charge in metastable
location within minerals. Illuminating the minerals and detrapping the charge that
combines at luminescence centers can determine the population of this charge. This
results in the emission of photons (luminescence). Artificially dosing sub-samples and
comparing the luminescence emitted with the natural luminescence can determine the
relationship between radiation flux and luminescence. The equivalent dose (D
E
)
experienced by the grains during burial therefore can be determined. The other quantity
needed to calculate the age is the ionizing radiation dose rate, which can be derived from
direct measurements or measured concentrations of radioisotopes. The age is then derived
using the equation:
Age = D
E
/dose rate
The uncertainty in the age is influenced by the systematic and random errors in the D
E

values and the possible temporal changes in the radiation flux. The quoted error is the
deviation of the D
E
values on multiple sub-samples and the error in measured ionizing
radiation dose rate or the concentration of radioisotopes. It is not possible to determine
temporal changes in the dose rate that is a consequence of changes in water content and
175

the growth and/or translocation of minerals within the sediment. The dose rate is
therefore generally assumed to have remained constant over time.
The collected sediment samples were processed in the Luminescence Dating
Laboratory at the University of Cincinnati. The USGS Reactor in Denver for neutron-
activation analysis (INAA) was utilized to determine the concentration of radioisotopes
for dose-rate determination. An uncertainty of 10% was applied to each of the determined
radioisotope concentrations to account possible micro-variation in concentration within
the sediment sample. The total in situ dose-rate from beta and gamma was determined by
converting elemental concentrations to beta and gamma dose-rates from Adamiec and
Aitken (1998) and applying the Beta attenuation factors for U, Th and K compositions
incorporating grain size factors from Mejdahl (1979). Beta attenuation factor for Rb was
taken as 0.75 (Adamiec and Aitken, 1998). Variable water content throughout the section
may have occurred throughout the history of the section. However, it is not possible to
determine the degree of such changes. The dose rate was therefore assumed to have
remained constant and a 10 ± 5% water content value was used to help account for
possible changes in water content. The dose-rate from cosmic rays was calculated
according to Prescott and Hutton (1994) and an uncertainty of ±10% is applied to account
for possible temporal changes. A summary of OSL dating results radioisotopes
concentrations, dose-rates, D
E
estimates and optical ages are provided in Table 1. The
radioisotope concentrations are within the normal range for naturally occurring sediments
with dose rates ranging from ~2.8 to 4.3 Gy/ka.
176

The remaining sediment in the center of the tube was dried in an oven at 50°C.
Particle-size fractions 90-125 µm, 125-180 µm, 180-250 µm, 250-500 µm, 500-1000 µm
and >1000 µm were obtained by dry-sieving the sediment. The carbonates and organic
matter were removed from the dominant fine-grained fraction (90-125 µm/125-180
µm/180-250 µm) using 10% HCl and 30% H
2
O
2
, respectively. The samples were then
treated with 10% HF for 20 minutes to dissolve fine feldspar, followed by 10% HCl for 2
hours to remove any fluorides. Lithium polytungstate solutions of different densities were
used to separate the quartz and feldspar-rich fractions from the heavy minerals. The
separated quartz-rich fraction was treated with 49% HF for 40-80 min to dissolve any
plagioclase feldspars and remove the alpha-irradiated surface of the quartz grains. Dried
quartz grains were mounted on stainless steel discs with silicon spray. All the preparation
techniques were carried out under laboratory safelights to avoid optical bleaching of the
luminescence signal.
Luminescence measurements were undertaken on quartz for the dominant particle
size for each sample using a Riso Automated TL/IRSL/Blue DA-15 C/D OSL Dating
System. Luminescence from the quartz grains was stimulated using an array of blue light
emitting diodes (470 nm, 50 mW/cm
2
) filtered using a green long-pass GG-420 filter.
Detection was through a Hoya U-340 filter. All quartz aliquots were screened for feldspar
contamination using infrared stimulation with infrared light emitting diodes (870 nm, 150
mW/cm
2
). All OSL signals were detected using a 52 mm diameter photomultiplier tube
(9235B). Riso Sequence Editor Software was used for hardware control.
177

Equivalent dose (D
E
) measurements were determined on multiple aliquots for
each sample using the single aliquot regenerative (SAR) method protocol developed by
Murray and Wintle (2000). The D
E
value for every aliquot of each sample was examined
using Riso Analysis 3.22b software. Preheat plateau tests were undertaken on samples
081507D and 081507G to determine a preheated temperature of 240
o
C. Dose recovery
tests were performed on each sample. Aliquots with poor recuperation (>10%) were not
used in the age calculations. In fluvial and colluvial sediments partial bleaching of
sediment is a problem, and this is reflected in a large spread of D
E
values and results in an
overestimate of the age. The weighted average of the D
E
values and its uncertainty were
therefore used in the final age calculation to help account for this issue. The weighted
average of the D
E
values distribution skews the average D
E
value the towards the younger
end of the range since the associated errors for older aliquots are greater, while at the
same time all the D
E
data is included in the calculation. The resultant age and its error,
therefore, provide the best representation of all the systematic and random errors.
However, the OSL age likely represents the maximum age for the deposition of the
sediment.

178

B3 Additional Photo Logs of the Paleoseismic Trenches on the Calico Fault

Figure B1 Detailed photo logs between meters 8-12 and meters 21-26 from the
northern (reversed) wall of the northern trench. (A) Detailed photo log of the main
(eastern) fault strand (between meters 8 and 9). Vertical separation of ~1 m with
younger units, 30-50, buttressing against the scarp of unit 70 plus a fissure fill
originating within unit 70, provide evidence for event horizon 3. Upward rupture
terminations between meter 10 and meter 12 provide evidence for the most recent
event. (B) Detailed photo log between meters 21 and meters 26. The upward
rupture terminations can be related to the penultimate event, however it is difficult
to discern their upward extent, and thus can be due to the most recent surface
rupture.
179

Figure B2 Evidence of three event horizons (A-C) comes from our northern trench, and evidence of the oldest
event horizon (D) comes from our southern trench. (A) Geometry of stratigraphic growth and upward
rupture terminations provide evidence in support of the most recent surface rupture. (B) Geometry of
stratigraphic growth of unit 50 and possible upward rupture termination within the same unit at meter 25
provide evidence in support of the penultimate event. (C) Vertical separation of ~1 m and fissure fills at the
bottom of unit 70 provide evidence in support of the anti-penultimate event. (D) Vertical separation of at least
1.5 m in our southern trench provides evidence in support of the oldest event horizon.
180

Figure B3 Photomosaic of (A) southern wall and (B) northern wall of the northern trench, and (C) southern
wall of the southern trench. The potential of trench collapse prevented us from photo-logging the northern
wall of the southern trench.

Abstract (if available)

Abstract The spatial and temporal strain accumulation and release patterns of faults remain an enigma, which has received an enormous amount of attention from geologists. Although the faults of the Eastern California shear zone (ECSZ), including the Garlock fault, are some of the most studied in the world, we still have only limited understanding of their role in the Pacific-North America plate boundary deformation. Geodetic models suggest that the right-lateral northwest-southeast striking ECSZ is the main fault system accumulating strain east of the San Andreas fault, while the left-lateral almost east-west striking Garlock fault has low strain accumulation rates. More geochronologically constrained slip rates are needed from the faults of the ECSZ and Garlock fault in order to determine whether strain storage and release are constant in this region. As part of this dissertation, I focused on several locations along the Garlock fault in southern California, and the Fish Lake Valley Fault (FLVF) in the northern part of the ECSZ, where I used Light Detection and Ranging (LiDAR) digital topographic data to measure normal fault scarps and restore offset alluvial fans to their pre-faulting positions. Combining those restorations with cosmogenic 10Be geochronology of the offset deposits, I was able to determine slip rates along the FLVF and Garlock fault systems.

Linked assets

University of Southern California Dissertations and Theses

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Asset Metadata

Creator Ganev, Plamen Nikolov (author)

Core Title Implications of new fault slip rates and paleoseismologic data for constancy of seismic strain release and seismic clustering in the eastern California shear zone

School College of Letters, Arts and Sciences

Degree Doctor of Philosophy

Degree Program Geological Sciences

Publication Date 11/03/2011

Defense Date 03/04/2011

Publisher University of Southern California (original), University of Southern California. Libraries (digital)

Tag active tectonics,Calico fault,eastern California shear zone,Fish Lake Valley fault,Garlock fault,geologic slip rates,Geomorphology,OAI-PMH Harvest,paleoseismology

Place Name California (states), fault zones: Calico fault (geographic subject), fault zones: eastern California shear zone (geographic subject), fault zones: Fish Lake Valley fault (geographic subject), fault zones: Garlock fault (geographic subject), USA (countries)

Language English

Contributor Electronically uploaded by the author (provenance)

Advisor Dolan, James F. (committee chair), Davis, Gregory A. (committee member), Frankel, Kurt L. (committee member), Hogen-Esch, Thieo E. (committee member)

Creator Email ganev@usc.edu,plamendry@yahoo.com

Permanent Link (DOI) https://doi.org/10.25549/usctheses-m3873

Unique identifier UC1132732

Identifier etd-Ganev-4417 (filename),usctheses-m40 (legacy collection record id),usctheses-c127-473718 (legacy record id),usctheses-m3873 (legacy record id)

Legacy Identifier etd-Ganev-4417.pdf

Dmrecord 473718

Document Type Dissertation

Rights Ganev, Plamen Nikolov

Type texts

Source University of Southern California (contributing entity), University of Southern California Dissertations and Theses (collection)

Repository Name Libraries, University of Southern California

Repository Location Los Angeles, California

Repository Email cisadmin@lib.usc.edu