HR: 1340h
AN: T43A-1388    [Abstracts]
TI: Interaction of Pacific and Philippine Sea Plates From V_p, V_s Tomography Under Kanto, Japan
AU: * Wu, F T
EM: wu@binghamton.edu
AF: State University of New York, Dept of Geological Sciences Vestal Pkwy E, Binghamton, NY 13902-6000 United States
AU: Okaya, D
EM: okaya@usc.edu
AF: University of Southern California, Dept of Earth Sciences, Los Angeles, CA 90089 United States
AU: Sato, H
EM: satow@eri.u-tokyo.ac.jp
AF: University of Tokyo, Earthquake Research Institute, Tokyo, 113-0032 Japan
AU: Hirata, N
EM: hirata@eri.u-tokyo.ac.jp
AF: University of Tokyo, Earthquake Research Institute, Tokyo, 113-0032 Japan
AB: The subduction of the Philippine Sea plate over the Pacific plate under the Kanto Plain is an unique plate tectonic system in the world. The recent densification of the seismic network in Kanto and the wide use of deep (~3 km) borehole and ocean bottom seismic sensors have created a high quality arrival times dataset from local shallow and intermediate earthquakes. Relatively high resolution (5km horizontal and 2 km vertical) seismic velocity tomography and relocated seismicity have been derived from these data. More details can therefore be seen than earlier, similarly comprehensive studies of Kanto (e.g., Ishida, 1992). The area of study is demarcated by latitudes 34^ON and 38^ON and longitudes 137^OE and 141^OE. Benz's tomography code (Benz et al.,1996 ) is employed. Within this area, while the geometry of the Pacific subduction zone appears clearly both in terms of velocity anomalies and associated double-layered seismicity, that of the Philippine Sea plate is quite complex. A few hundred kilometers to the west of Izu Peninsula, the subducting plate is marked by well defined gently dipping seismic and higher velocity zones. Within a few hundred kilometers to the west of Izu Peninsula however there is no clear Wadata-Benioff zone nor high velocity anomalies to help define PSP. Yet on the east side a well defined WBZ with an anomalous seismic zone can readily be seen and it nearly bottomed on top of the Pacific subduction zone. Well-defined WBZ continues eastward but as the Pacific zone gets shallower the segment of PSP subduction zone gets shorter as they all bottom against the Pacific plate. and that the number of segments of PSP increase as the tip of the Pacific mantle wedge is approached. The V_p and V_s ratios, in combination with the V_p allows us to explore the possible petrology (Christensen, 1996) associated with the tectonic processes in the area.
DE: 7209 Earthquake dynamics (1242)
DE: 7299 General or miscellaneous
DE: 8120 Dynamics of lithosphere and mantle: general (1213)
DE: 8123 Dynamics: seismotectonics
DE: 8124 Earth's interior: composition and state (1212, 7207, 7208, 8105)
SC: Tectonophysics [T]
MN: Fall Meeting 2005