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OBSERVATIONS AND MODELING OF DYNAMICALLY TRIGGERED HIGH
FREQUENCY BURST EVENTS
by
Adam David Fischer
A Dissertation Presented to the
FACULTY OF THE GRADUATE SCHOOL
UNIVERSTIY OF SOUTHERN CALIFORNIA
In Partial Fulfillment of the
Requirements for the Degree
DOCTOR OF PHILOSOPHY
(EARTH SCIENCES)
DECEMBER 2008
Copyright 2008 Adam David Fischer
Object Description
| Title | Observations and modeling of dynamically triggered high frequency burst events |
| Author | Fischer, Adam David |
| Author email | adfische@usc.edu; geophysicsman@gmail.com |
| Degree | Doctor of Philosophy |
| Document type | Dissertation |
| Degree program | Geological Sciences |
| School | College of Letters, Arts and Sciences |
| Date defended/completed | 2008-10-17 |
| Date submitted | 2008 |
| Restricted until | Unrestricted |
| Date published | 2008-10-31 |
| Advisor (committee chair) | Sammis, Charles G. |
| Advisor (committee member) |
Nutt, Steven Ben-Zion, Yehuda Teng, Ta-Liang Becker, Thorsten |
| Abstract | A series of high-frequency (>20Hz) bursts of energy are observed on strong motion records during the 1999 Chi-Chi, Taiwan Earthquake Mw7.6. We hypothesized that these bursts originated near the individual stations as small, shallow events that were dynamically triggered by the P- and S-waves generated by the Chi-Chi mainshock. These bursts were originally interpreted as a mainshock source signal by Chen et al., [2006] but our observations of events on strong motion records recorded at stations up to 170 km from the mainshock epicenter is consistent with the local triggering hypothesis. If the bursts originated on the Chi-Chi fault plane, as hypothesized by Chen et al. [2006] based on their analysis of recordings within 20Km from the Chelungpu fault, then they should not be observable at this distance assuming any reasonable value of crustal attenuation. The bursts on all strong motion stations in the Taiwan Central Weather Bureau network (TWCB) were identified using a numerical algorithm approach. This data set was analyzed in the context of local dynamic triggering which resulted in a stress threshold for triggering in the range 0.03 to 0.05 MPa for S-wave triggering and 0.0013 to 0.0033 MPa for P-wave triggering, consistent with prior observations of surface wave triggering.; In an attempt to better characterize the nature of high frequency bursts, similar analysis of strong motion records was performed on the records of the 2004 Parkfield, CA earthquake (Mw6) at the USGS UPSAR array. The average array spacing was relatively small compared to the instruments in Taiwan so that further constraint of the location of bursts was possible. Bursts were found to be incoherent even for stations spaced 40m apart, suggesting that they occur in a region approximately 20m from the stations. The triggering threshold was found to be ~0.02Mpa, consistent with the observations from Taiwan.; To test the possibility of nucleating unstable slip events in the very shallow crust we modeled what is now referred to as "dynamic driving" of high frequency burst events through numerical simulation. Rate-and-state friction presented a paradox for the nucleation of such shallow events but we have determined that tensile stresses due to mode conversion at the free surface of the earth allow for nucleation of unstable slip that can produce radiation recorded as high-frequency bursts. |
| Keyword | seismology; earthquakes; Parkfield; Taiwan; Chi-Chi; dynamic triggering; earthquake interaction; observation; modeling; high frequency; bursts; attenuation; seismic waves; secondary radiation |
| Geographic subject | faults: Chelungpu fault |
| Geographic subject (city or populated place) | Chi-Chi; Parkfield |
| Geographic subject (state) | California |
| Geographic subject (country) | Taiwan |
| Coverage date | 1999; 2004 |
| 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-m1738 |
| Rights | Fischer, Adam David |
| 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-Fischer-2506 |
| Archival file | uscthesesreloadpub_Volume44/etd-Fischer-2506.pdf |
Description
| Title | Page 1 |
| Full text | OBSERVATIONS AND MODELING OF DYNAMICALLY TRIGGERED HIGH FREQUENCY BURST EVENTS by Adam David Fischer A Dissertation Presented to the FACULTY OF THE GRADUATE SCHOOL UNIVERSTIY OF SOUTHERN CALIFORNIA In Partial Fulfillment of the Requirements for the Degree DOCTOR OF PHILOSOPHY (EARTH SCIENCES) DECEMBER 2008 Copyright 2008 Adam David Fischer |
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