HR: 17:00h
AN: S54A-05    [Abstracts]
TI: Relocations and 3-D Velocity Structure for Aftershocks of the 2000 W. Tottori (Japan) Earthquake and 2001 Gujarat (India) Earthquake, Using Waveform Cross-correlations
AU: * Enescu, B
EM: benescu@rcep.dpri.kyoto-u.ac.jp
AF: Research Center for Earthquake Prediction, Disaster Prevention Research Institute, Kyoto University, Gokasho, Uji, Kyoto, 611-0011 Japan
AU: Mori, J
EM: mori@rcep.dpri.kyoto-u.ac.jp
AF: Research Center for Earthquake Prediction, Disaster Prevention Research Institute, Kyoto University, Gokasho, Uji, Kyoto, 611-0011 Japan
AB: The newly developed double-difference tomography method (Zhang and Thurber,2003) makes use of both absolute and relative arrival times to produce an improved velocity model and highly accurate hypocenter locations. By using this technique, we relocate the aftershocks of the 2000 Western Tottori earthquake (Mw 6.7) and 2001 Gujarat (Mw 7.7) earthquake and obtain a 3D-velocity model of the aftershock region. The first data set consists of 1035 aftershocks recorded at 62 stations during a period of about a month following the mainshock (Shibutani et al.,2002). In order to get the best arrival times a cross-correlation analysis was used to align the waveforms. The epicentral distribution of the relocated events reveals clear earthquake lineations, some of them close to the mainshock, and an increased clustering. The aftershocks' depth distribution shows a mean shift of the hypocenters' centroid of about 580m; a clear upper cutoff of the seismic activity and some clustering can be also seen. The final P-wave velocity model shows higher-value anomalies in the vicinity of the mainshock's hypocenter, in good agreement with the results of Shibutani et al.(2004). The second data set consists of about 1300 earthquakes, recorded during one week of observations by a Japanese-Indian research team in the aftershock region of the Gujarat earthquake (Sato et al.,2001). Using the double-difference algorithm and waveform cross-correlations, we were able to identify a more clear alignment of hypocenters that define the mainshock's fault and an area of relatively few aftershocks in the region of the mainshock's hypocenter. Both studies demonstrate that the cross-correlation techniques applied for events with inter-event distances as large as 10km and cross correlation coefficients as low as 50% can produce more accurate locations than those determined from catalog phase data. We are going to discuss briefly the critical role of frequency filtering and of the time window used for cross-correlation on the relocation results. To facilitate the data processing tasks we have developed a GUI oriented, Matlab-based toolbox.
UR: http://www.rcep.dpri.kyoto-u.ac.jp/$^{\sim}$benescu/
DE: 8180 Tomography
DE: 7230 Seismicity and seismotectonics
DE: 7205 Continental crust (1242)
DE: 7215 Earthquake parameters
SC: Seismology [S]
MN: 2004 AGU Fall Meeting