HR: 13:40h
AN: S53C-01    [Abstracts]
TI: Imaging the fault plane and asperities of the 1995 southern Hyogo (Kobe) earthquake (M7.3) by double-difference tomography
AU: * Okada, T
EM: okada@aob.geophys.tohoku.ac.jp
AF: Research Center for Prediction of Earthquakes and Volcanic Eruptions, Graduate School of Science, Tohoku University, 6-6 Aramaki-Aza-Aoba, Aoba-ku, Sendai, 9808578 Japan
AU: Hasegawa, A
EM: hasegawa@aob.geophys.tohoku.ac.jp
AF: Research Center for Prediction of Earthquakes and Volcanic Eruptions, Graduate School of Science, Tohoku University, 6-6 Aramaki-Aza-Aoba, Aoba-ku, Sendai, 9808578 Japan
AU: Suganomata, J
EM: suga@aob.geophys.tohoku.ac.jp
AF: Research Center for Prediction of Earthquakes and Volcanic Eruptions, Graduate School of Science, Tohoku University, 6-6 Aramaki-Aza-Aoba, Aoba-ku, Sendai, 9808578 Japan
AU: Zhao, D
EM: zhao@sci.ehime-u.ac.jp
AF: Geodynamics Research Center, Ehime University, 2-5 Bunkyo-cho, Matsuyama, 7908577 Japan
AU: Zhang, H
EM: hjzhang@ice.geology.wisc.edu
AF: Department of Geology and Geophysics, University of Wisconsin-Madison, 1215 W Dayton Street, Madison, WI 53706 United States
AU: Thurber, C
EM: clifft@ice.geology.wisc.edu
AF: Department of Geology and Geophysics, University of Wisconsin-Madison, 1215 W Dayton Street, Madison, WI 53706 United States
AB: The nature of the large slip areas (asperities) of the fault is uncertain. Asperities are common in the case of some large or moderate-sized interplate recurrent earthquake pairs along the plate boundary in NE Japan (Okada et al., 2003, Yamanaka and Kikuchi, 2003, Hasegawa et al., 2004, Matsuzawa et al., 2004). These observations suggest that the asperities are persistent features that would reflect some physical properties on the fault plane. To study this phenomenon, we obtained the seismic velocity structure around the fault plane of the 1995 southern Hyogo (Kobe) earthquake (M7.3) in southwestern Japan. We adopted the double-difference (DD) tomography method (Zhang and Thurber, 2003), which has the advantage of obtaining the high-resolution seismic velocity structure in and around the focal area. The inversion uses 23,228 P-wave and 18,902 S-wave arrival times from 915 earthquakes recorded by a dense temporary seismic network (Hirata et al., 1996) for aftershocks and seismic networks routinely operated by Kyoto University, University of Tokyo and Kochi University. We inverted the velocity model with a grid interval of 3 km in and around the focal area. Obtained results are summarized as follows: (1) Low velocity zones of a few kilometers wide are distributed along the fault or along the aftershock alignment. This suggests that the fault plane of the present earthquake is located in a low velocity zone. (2) The velocities of this low velocity zone vary along the strike of the fault plane. We compared the seismic velocity distribution along the fault plane with the slip distribution obtained by seismic and geodetic inversions (Yoshida et al., 1996). Large slip areas (asperities) correspond to relatively high velocity areas on the fault plane. We also have obtained the seismic velocity model in and around the focal area of other two large shallow inland earthquakes (2000 M7.3 western Tottori and 2003 M6.4 northern Miyagi earthquakes) that occurred recently in Japan, using DD tomography. The correspondence between asperities and high velocity zones was also observed for these two events.
UR: http://www.aob.geophys.tohoku.ac.jp/~okada
DE: 8180 Tomography
DE: 8010 Fractures and faults
DE: 8015 Local crustal structure
DE: 8123 Dynamics, seismotectonics
DE: 7209 Earthquake dynamics and mechanics
SC: Seismology [S]
MN: 2004 AGU Fall Meeting