HR: 0800h
AN: S21A-0201    [Abstracts]
TI: Configuration of the Philippine Sea Plate Beneath Kanto, 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
S21A-0201 AF: Earthquake Research Institute, University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo, 113-0032 Japan
AU: Koketsu, K
S21A-0201 AF: Earthquake Research Institute, University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo, 113-0032 Japan
AU: Kobayashi, R
S21A-0201 AF: Earthquake Research Institute, University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo, 113-0032 Japan
AU: Matsubara, M
S21A-0201 AF: National Research Institute for Earth Science and Disaster Prevention, 3-1 Tennodai, Tsukuba, 305-0006 Japan
AU: Kimura, H
S21A-0201 AF: National Research Institute for Earth Science and Disaster Prevention, 3-1 Tennodai, Tsukuba, 305-0006 Japan
AU: Iwasaki, T
S21A-0201 AF: Earthquake Research Institute, University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo, 113-0032 Japan
AU: Kasahara, K
S21A-0201 AF: National Research Institute for Earth Science and Disaster Prevention, 3-1 Tennodai, Tsukuba, 305-0006 Japan
AB: Devastating earthquakes occur on a mega-thrust fault that underlies the Tokyo metropolitan region. In order to identify this fault, which is the upper surface of the Philippine Sea plate (PSP), we have conducted a series of active and passive seismic experiments which includes a deep seismic reflection and wide-angle-reflection/refraction profiling on four lines and array observation of earthquakes. From the controlled source experiment we found that the depth to the top of this plate, 4 to 26 km, is much shallower than previous estimates based on the distribution of seismicity. The result is consistent with the newly developed tomographic images from earthquake data. In the Kanto district we observed small repeating earthquakes which are interpreted to occur on the plate boundary. The spatial distribution of the repeating earthquakes revealed the upper boundary of the PSH in the eastern Kanto district where the plate had a flat geometry. We correlated the location of the repeating earthquakes to the reflection horizon to find that the earthquakes are slightly deeper than the reflector, which suggest that a slip boundary is located on the bottom of the reflective low velocity layer revealed by the reflection survey. The shallower plate geometry changes the location of maximum finite slip of the 1923 Kanto earthquake and will affect estimations of strong ground motion for seismic hazards analysis within the Tokyo region. The source area of the1855 Ansei-Edo Earthquake is also need to be modified according to our new plate model.
UR: http://www.eri.u-tokyo.ac.jp/daidai/index-J.html
DE: 0935 Seismic methods (3025, 7294)
DE: 7230 Seismicity and tectonics (1207, 1217, 1240, 1242)
DE: 7270 Tomography (6982, 8180)
SC: Seismology [S]
MN: Fall Meeting 2005