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SEISMICITY DISTRIBUTION NEAR STRIKE-SLIP FAULTS
IN CALIFORNIA
by
Peter Marion Powers
A Dissertation Presented to the
FACULTY OF THE GRADUATE SCHOOL
UNIVERSITY OF SOUTHERN CALIFORNIA
In Partial Fulfillment of the
Requirements for the Degree
DOCTOR OF PHILOSOPHY
(GEOLOGICAL SCIENCES)
August 2009
Copyright 2009 Peter Marion Powers
Object Description
| Title | Seismicity distribution near strike-slip faults in California |
| Author | Powers, Peter Marion |
| Author email | pmpowers@usc.edu; geowerks@gmail.com |
| Degree | Doctor of Philosophy |
| Document type | Dissertation |
| Degree program | Geological Sciences |
| School | College of Letters, Arts and Sciences |
| Date defended/completed | 2009-04-17 |
| Date submitted | 2009 |
| Restricted until | Unrestricted |
| Date published | 2009-06-04 |
| Advisor (committee chair) | Jordan, Thomas H. |
| Advisor (committee member) |
Dolan, James F. Sammis, Charles G. Ghanem, Roger G. |
| Abstract | Hypocenters of small, relocated earthquakes are used to constrain how seismicity rates vary with distance from strike-slip faults in California. Stacks of events in a fault-referenced coordinate system show that out to a fault-normal distance x of 3-6 km, seismicity obeys a power-law ~(1+x^2/d^2)^(-g/2), where g is the asymptotic roll-off rate and d is a near-fault inner scale. These results are compatible with a 'rough fault loading' model in which the inner scale d measures the half-width of a volumetric damage zone and the roll-off rate g is governed by stress variations due to fault roughness. Two-dimensional numerical simulations by J. Dieterich and D. Smith indicate that g is approximately equal to the fractal dimension of along-strike roughness. Results of a multi-catalog error analysis and catalog simulations are used to correct the estimates of g and d for mislocation bias. Near-fault seismicity is more localized on faults in Northern California (NoCal: d=50±20m, g=1.51±0.05) than in Southern California (SoCal: d=210±40m, g=0.97±0.05). The Parkfield region has a damage-zone half-width (d=120±30m) consistent with the SAFOD drilling estimate and its high roll-off rate (g=2.30±0.25) indicates a relatively flat roughness spectrum: ~k^-1 vs. ~k^-2 for NoCal and ~k^-3 for SoCal. Fault surfaces in SoCal are therefore nearly self-similar, and their roughness spectra are redder than in NoCal, consistent with the macroscopic complexity of the observed fault traces. The damage-zone widths -- the first direct estimates averaged over the seismogenic layer -- can be interpreted in terms of an across-strike 'fault-core multiplicity' that is ~1 in NoCal, ~2 at Parkfield, and ~3 in SoCal.; The localization of seismicity near individual faults correlates with cumulative offset, seismic productivity, and aseismic slip, consistent with a model in which faults originate as branched networks with broad, multi-core damage zones and evolve towards more localized, lineated features with low fault-core multiplicity, thinner damage zones, and less seismic coupling. The spatial distribution of aftershocks is modified by the presence of faults and is well described by an elliptical kernel, in which an aspect parameter scales with distance from a fault. |
| Keyword | earthquakes; microseismicity; strike-slip faults; earthquake forecasting; earthquake triggering; statistical seismology; fault evolution; fault models |
| Geographic subject (state) | California |
| Language | English |
| Part of collection | University of Southern California dissertations and theses |
| Publisher (of the original version) | University of Southern California |
| Place of publication (of the original version) | Los Angeles, California |
| Publisher (of the digital version) | University of Southern California. Libraries |
| Provenance | Electronically uploaded by the author |
| Type | texts |
| Legacy record ID | usctheses-m2283 |
| Rights | Powers, Peter Marion |
| Repository name | Libraries, University of Southern California |
| Repository address | Los Angeles, California |
| Repository email | http://www.usc.edu/isd/libraries/services/ask_a_librarian/email/ |
| Filename | etd-Powers-2914 |
| Archival file | uscthesesreloadpub_Volume44/etd-Powers-2914.pdf |
Description
| Title | Page 1 |
| Full text | SEISMICITY DISTRIBUTION NEAR STRIKE-SLIP FAULTS IN CALIFORNIA by Peter Marion Powers A Dissertation Presented to the FACULTY OF THE GRADUATE SCHOOL UNIVERSITY OF SOUTHERN CALIFORNIA In Partial Fulfillment of the Requirements for the Degree DOCTOR OF PHILOSOPHY (GEOLOGICAL SCIENCES) August 2009 Copyright 2009 Peter Marion Powers |
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