HR: 13:55h
AN: T33E-02    [Abstracts]
TI: Crustal Structure Using the Tomography Method, in the Central Part of Itoigawa-Shizuoka Tectonic Line (ISTL), Japan
AU: * Panayotopoulos, Y
EM: yannis@eri.u-tokyo.ac.jp
AF: Earthquake Research Institute,Tokyo University, 1-1-1 Yayoi, Bunkyo ward, Tokyo, 113-0032 Japan
AU: Hirata, N
T33E-02 AF: Earthquake Research Institute,Tokyo University, 1-1-1 Yayoi, Bunkyo ward, Tokyo, 113-0032 Japan
AU: Takeda, T
T33E-02 AF: National Research Institute for Earth Science and Disaster Prevention, 3-1 Tennodai, Tsukuba, Ibaraki, 305-0006 Japan
AU: Kato, A
T33E-02 AF: Earthquake Research Institute,Tokyo University, 1-1-1 Yayoi, Bunkyo ward, Tokyo, 113-0032 Japan
AU: Kurashimo, E
T33E-02 AF: Earthquake Research Institute,Tokyo University, 1-1-1 Yayoi, Bunkyo ward, Tokyo, 113-0032 Japan
AU: Iwasaki, T
T33E-02 AF: Earthquake Research Institute,Tokyo University, 1-1-1 Yayoi, Bunkyo ward, Tokyo, 113-0032 Japan
AB: The central part of the Itoigawa-Shizuoka Tectonic Line (ISTL) plays a crucial factor in understanding the tectonic evolution of the ISTL fault system. The ISTL is located in the centre of Honshu Island of Japan and forms a tectonic boundary that divides Japan in NE and SW parts. During the Pliocene it was reactivated as a reverse fault due to tectonic inversion after the collision of the Izu-Bonin arc with the Japanese arc. Presently the northern part of ISTL behaves as a low angle east dipping thrust fault and the southern-central part as a west dipping thrust fault. A temporary network consisting of 49 linear array stations cutting across the ISTL fault trace and 9 stations scattered in the surrounding area, was deployed for a 2 month period from 25 Aug. to 16 Oct. 2003. Combining our temporary network with the permanent network in this area, we determined several local events. We analysed these events to locate and reveal the velocity structure across the ISTL, and connect them with seismic activity which may be related to present time movements of the fault system. The tomography method was applied to 69 earthquakes and 2 vibroseis shots in the central part of ISTL. We have obtained 3523 P and 2907 S wave arrival time data, picked at 79 stations. We processed these events to reveal the velocity structure across the ISTL. In the Vp cross-section we image 2 areas with low Vp values at the NE and Central parts. We have achieved good P wave resolution at 0-12 Km depths for a 40 Km long area of the cross-section, with P rms residuals dropping from 0.324 to 0.125 s. These low Vp zones can be identified on the geological map as the Yatsugatake volcano depositions and the marginal depositions of the Japanese arc. The ISTL is estimated to be on the boundary between the low Vp zone of the margins and the high Vp zone of the Izu-Bonin arc rocks. Due to the large lateral heterogeneities, the relocated events are estimated to be 2-3 km shallower than the events published by the Japanese Meteorological Agency. Most of the events in the profile are located below the ISTL fault plane, thus we can_ft attribute them to present time activity of the fault system.
DE: 7230 Seismicity and tectonics (1207, 1217, 1240, 1242)
DE: 7270 Tomography (6982, 8180)
SC: Tectonophysics [T]
MN: Fall Meeting 2005