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Seismic evidence for rock damage and healing on the San Andreas Fault associated with the 2004 M 6.0 Parkfield earthquake

Yong-Gang Li, Po Chen, Elizabeth S. Cochran, John E. Vidale and Thomas Burdette
Seismic evidence for rock damage and healing on the San Andreas Fault associated with the 2004 M 6.0 Parkfield earthquake (in Special issue on the 2004 Parkfield earthquake and the Parkfield Earthquake Prediction Experiment, Ruth A. Harris (prefacer) and J. Ramon Arrowsmith (prefacer))
Bulletin of the Seismological Society of America (September 2006) 96 (4B): S349-S363

Abstract

We deployed a dense linear array of 45 seismometers across and along the San Andreas fault near Parkfield a week after the M 6.0 Parkfield earthquake on 28 September 2004 to record fault-zone seismic waves generated by aftershocks and explosions. Seismic stations and explosions were co-sited with our previous experiment conducted in 2002. The data from repeated shots detonated in the fall of 2002 and 3 months after the 2004 M 6.0 mainshock show approximately 1.0%-1.5% decreases in seismic-wave velocity within an approximately 200-m-wide zone along the fault strike and smaller changes (0.2%-0.5%) beyond this zone, most likely due to the coseismic damage of rocks during dynamic rupture in the 2004 M 6.0 earthquake. The width of the damage zone characterized by larger velocity changes is consistent with the low-velocity waveguide model on the San Andreas fault, near Parkfield, that we derived from fault-zone trapped waves (Li et al., 2004). The damage zone is not symmetric but extends farther on the southwest side of the main fault trace. Waveform cross- correlations for repeated aftershocks in 21 clusters, with a total of approximately 130 events, located at different depths and distances from the array site show approximately 0.7%-1.1% increases in S-wave velocity within the fault zone in 3 months starting a week after the earthquake. The velocity recovery indicates that the damaged rock has been healing and regaining the strength through rigidity recovery with time, most likely due to the closure of cracks opened during the mainshock. We estimate that the net decrease in seismic velocities within the fault zone was at least approximately 2.5%, caused by the 2004 M 6.0 Parkfield earthquake. The healing rate was largest in the earlier stage of the postmainshock healing process. The magnitude of fault healing varies along the rupture zone, being slightly larger for the healing beneath Middle Mountain, correlating well with an area of large mapped slip. The fault healing is most prominent at depths above approximately 7 km.


ISSN: 0037-1106
EISSN: 1943-3573
Coden: BSSAAP
Serial Title: Bulletin of the Seismological Society of America
Serial Volume: 96
Serial Issue: 4B
Title: Seismic evidence for rock damage and healing on the San Andreas Fault associated with the 2004 M 6.0 Parkfield earthquake
Title: Special issue on the 2004 Parkfield earthquake and the Parkfield Earthquake Prediction Experiment
Author(s): Li, Yong-GangChen, PoCochran, Elizabeth S.Vidale, John E.Burdette, Thomas
Author(s): Harris, Ruth A.prefacer
Author(s): Arrowsmith, J. Ramonprefacer
Affiliation: University of Southern California, Department of Earth Sciences, Los Angeles, CA, United States
Affiliation: U. S. Geological Survey, Menlo Park, CA, United States
Pages: S349-S363
Published: 200609
Text Language: English
Publisher: Seismological Society of America, Berkeley, CA, United States
References: 57
Accession Number: 2006-075802
Categories: SeismologyStructural geology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. geol. sketch maps
N35°40'00" - N36°00'00", W120°34'60" - W120°10'00"
Secondary Affiliation: Arizona State University, USA, United StatesScripps Institution of Oceanography, USA, United StatesUniversity of California at Los Angeles, USA, United StatesU. S. Geological Survey, USA, United States
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Abstract, Copyright, Seismological Society of America. Reference includes data from GeoScienceWorld, Alexandria, VA, United States
Update Code: 200643
Program Name: USGSOPNon-USGS publications with USGS authors
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