HR: 17:30h
AN: S44A-07    [Abstracts]
TI: Seismic imaging of the 1923 Kanto Earthquake Source Area on the subducting Philippine Sea plate, in Japan
AU: * Hirata, N
EM: hirata@eri.u-tokyo.ac.jp
AF: Earthquake Research Institute, University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo, 113-0032 Japan
AU: Sato, H
EM: satow@eri.u-tokyo.ac.jp
AF: Earthquake Research Institute, University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo, 113-0032 Japan
AU: Koketsu, K
AF: Earthquake Research Institute, University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo, 113-0032 Japan
AU: Okaya, D
AF: University of Southern California, Los Angeles, LA, CA 90089-0740 United States
AU: Iwasaki, T
AF: Earthquake Research Institute, University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo, 113-0032 Japan
AU: Ito, T
AF: Chiba Univ., Yayoi, Chiba, 263-8522 Japan
AU: Kasahara, K
AF: NIED, Tsukuba, Tsukuba, 305-0006 Japan
AU: Ikawa, T
AF: JGI Inc, Bunkyo, Tokyo, 112-0012 Japan
AU: Abe, S
AF: JGI Inc, Bunkyo, Tokyo, 112-0012 Japan
AU: Kawanaka, T
AF: JGI Inc, Bunkyo, Tokyo, 112-0012 Japan
AU: Matsubara, M
AF: Chiba Univ., Yayoi, Chiba, 263-8522 Japan
AU: Matsubara, M
AF: NIED, Tsukuba, Tsukuba, 305-0006 Japan
AU: Harder, S
AF: Univ. of Texas El Paso, El Paso, El Paso, TX 79968-0555 United States
AB: Large devastating earthquakes sometimes occur on a mega-thrust source fault which underlies the Tokyo metropolitan region. The source faults are located on the upper boundary of the subducting the Philippine Sea plate (PSP), which was so far estimated mainly from seismicity distribution. To get better prediction of the strong ground motion, we need to precisely characterize the source fault of those large earthquakes. A depth and geometry of the PSP is a key for characterization. We deployed four controlled source seismic lines in the Kanto area from 2002 to 2003: The 150-km long Boso line in 2002, the 80-km Sagami line in 2003, the 80-km Tokyo Bay line in 2003, and the 165-km Eastern part of the Kanto Mountain line in 2003. We, for the first time, directly identify the source fault using deep seismic reflection profiling images to be the upper surface of the PSP, which is found to be much shallower than previous indirect estimation based on seismicity distribution by 10 to 20 km. This geometry serves as a new constraint for studies of Kanto seismotectonics and seismic imaging using earthquakes such as high resolution 3D tomography and receiver function analysis. In the seismic profiles, we also found that highly reflective zones correspond to regions of silent slip plus areas outside the asperity zones of the 1923 Kanto earthquake. We propose that an asperity on a plate boundary can be detected by an evaluation of its reflectivity and represents possible regions of rupture for future earthquakes. Together with the obtained velocity structure, our result provides the essential control for the research on crustal deformation, modeling of source fault and strong ground motion estimation.
DE: 7223 Seismic hazard assessment and prediction
DE: 7218 Lithosphere and upper mantle
SC: Seismology [S]
MN: 2004 AGU Fall Meeting