HR: 0800h
AN: T51C-0679    [Abstracts]
TI: Analysis of fault zone head waves in the San Andreas and Southwest Fracture Zone around the hypocenter of the 2006 M6 Parkfield earthquake
AU: * Shi, Z
EM: zheqians@usc.edu
AF: Department of Earth Sciences, University of Southern California, 3651 Trousdale Pkwy, Los Angeles, CA 90089, United States
AU: Ben-Zion, Y
EM: benzion@usc.edu
AF: Department of Earth Sciences, University of Southern California, 3651 Trousdale Pkwy, Los Angeles, CA 90089, United States
AU: Peng, Z
EM: zhigang.peng@eas.gatech.edu
AF: School of Earth and Atmospheric Sciences, Georgia Institute of Technology, 311 Ferst Drive, Atlanta, GA 30332, United States
AU: Lewis, M
EM: malewis@usc.edu
AF: Department of Earth Sciences, University of Southern California, 3651 Trousdale Pkwy, Los Angeles, CA 90089, United States
AU: Zhao, P
EM: pzhao@gatech.edu
AF: School of Earth and Atmospheric Sciences, Georgia Institute of Technology, 311 Ferst Drive, Atlanta, GA 30332, United States
AB: We investigate the velocity contrast along the Parkfield section of the San Andreas fault (SAF) and the Southwest Fracture Zone (SWFZ) near the hypocenter of the 2006 M6 Parkfield earthquake by analyzing fault zone head waves (FZHW) that refract along the bimaterial fault interface (Ben-Zion, 1989). This study is a component of a larger project on imaging bimaterial interfaces in the Parkfield region with multiple seismic networks. The employed dataset has 1282 events recorded by the 2004 Parkfield Guided Wave Experiment (Michael et al., 2005) during the period of October 2004 to January 2005. This temporary network has 15 stations with L22 short-period sensors that are arranged in pairs on the main traces of the SAF and SWFZ. Due to the close proximity of the stations to the faults, complicated fault-zone-related phases are present in most waveforms. For accurate identification of FZHW and P wave arrivals, only waveforms with very high signal-to-noise ratios are used. By assuming right-lateral strike-slip focal mechanisms for all the events, we align the first peak or trough of the P wave arrival and examine the moveout of head wave with increasing along-fault propagation distance. So far we have identified clear FZHW signals at stations NE1O (near Gold Hill) and NE2O (near Parkfield Bridge), located within 100 m from the SAF, for propagation path along the SAF between SAFOD and Gold Hill. Analysis of head wave moveouts at these stations indicates small average velocity contrast in the immediate vicinity of the SAF between Middle Mountain and Gold Hill: ~4% contrast near Middle Mountain and ~3% near Gold Hill. Cross- section views of the seismicity reveal two concentrated bands of earthquakes: a shallower band around a depth of 5 km and a deeper band around a depth of 10 km. Head wave analysis of these two separate groups of events shows an increase of the velocity contrast with depth. The obtained results may reflect the velocity contrast between the NE bounding block and a damage zone generated by the 2004 event, as the employed stations are very close to the SAF. Analysis of the waveforms recorded at stations across the SWFZ is currently in progress.
DE: 0710 Periglacial processes
DE: 7205 Continental crust (1219)
DE: 7270 Tomography (6982, 8180)
DE: 7294 Seismic instruments and networks (0935, 3025)
DE: 7299 General or miscellaneous
SC: Tectonophysics [T]
MN: 2007 Fall Meeting