HR: 0800h
AN: S41A-0921    [Abstracts]
TI: Fault Structure from Double-difference Relocations and Waveform Modeling of Aftershocks of the 1992 Landers Earthquake
AU: * Li, H
EM: lih@eas.slu.edu
AF: Earth and Atmospheric Sciences Department, Saint Louis University, 3507 Laclede Ave. #3F, Saint Louis, MO 63103 United States
AB: Aftershocks can provide multiple information for investigating fault zone structure. We used the double-difference (DD) method to determine high-resolution hypocenters of 140 aftershocks of the 1992 Landers, California, $M_W$ = 7.3 earthquake. The DD technique incorporates catalog travel time data and differential travel times from waveform cross-correlation of P- and S-waves. To understand better fault zone geometry and material properties, we performed body wave waveform modeling for 9 aftershocks recorded by a dense seismic array cross the rupture zone of the 1992 Landers earthquake. A forth-order staggered-grid three-dimensional (3D) finite difference (FD) method is used to generate synthetic waveforms. Wave propagations in a 3D medium are computed up to 20 Hz with grid space 15 m. Different fault zone geometry (fault zone depth, width, azimuth) and material properties (vp/vs ratio, wave velocities of the fault zone and host rock) are tested. Waveform modeling results indicate that a wedge-shaped strucutre with depth of approximately 2-3km, width of approximately 100 m, P-wave velocity reduction relative to the host rock of about 50 percent and vp/vs ratio of approximately 4.0 in fault zone is responsible for travel time delay and waveform distortion. The structure follows the strike of surface trace of the rupture. The waveform modeling also implies that the structure is not symmetric to the surface trace and centered about 50 m east of the surface break.
DE: 7230 Seismicity and seismotectonics
SC: Seismology [S]
MN: 2004 AGU Fall Meeting