HR: 1340h
AN: T33B-0549    [Abstracts]
TI: Seismic structure of the subducting Philippine Sea slab beneath southwestern Japan
AU: * Iidaka, T
EM: iidaka@eri.u-tokyo.ac.jp
AF: Earthquake Research Institute, University of Tokyo, Yayoi 1-1-1, Bunkyo, Tokyo, 113-0032 Japan
AU: Igarashi, T
EM: igarashi@eri.u-tokyo.ac.jp
AF: Earthquake Research Institute, University of Tokyo, Yayoi 1-1-1, Bunkyo, Tokyo, 113-0032 Japan
AU: Iwasaki, T
EM: iwasaki@eri.u-tokyo.ac.jp
AF: Earthquake Research Institute, University of Tokyo, Yayoi 1-1-1, Bunkyo, Tokyo, 113-0032 Japan
AB: Understanding of the shape and characteristics of subducting slabs is very important to know the mechanism of interplate earthquakes and process of the subduction. The configuration of the subducting slab had been obtained at the western part of southwestern Japan by receiver function methods. At the eastern part of southwestern Japan, however, the configuration of the Philippine Sea slab has not yet been obtained. Spatially high-dense array with 40 seismic stations had been operated for two years at the southwestern Japan. The following processes are applied to the waveforms: 1) the radial component of the waveform is obtained; 2) the amplitude of the waveform is normalized and band-pass filtered; 3) the envelope is calculated and the envelope is squared to emphasize the later phases; 4) the waveform envelopes are stacked at each seismic station for the earthquakes occurring in a cluster. An analysis using a spatially highly dense array makes it possible to detect the converted phase at the upper boundary of the Philippine Sea slab. A weak signal can be detected by the waveform stacking process, resulting in observation of the PS converted phase at the subducting Philippine Sea slab. Two converted phases are observed using the seismic array at the eastern part of southwestern Japan. One is clear later phase with large amplitude, the other is its precursor with small amplitude, which is 1 sec earlier than the clear later phase. We interpret that the clear later phase is the converted wave at the bottom of the oceanic crust of the subducting Philippine Sea slab; the other is the converted wave at the top of the slab. The configuration of the subducting Philippine Sea slab is obtained at a depth range of 50 km - 75 km. The subducting Philippine Sea plate had not been detected in the area by previous studies. This study indicates that the waveform stacking method of the cluster earthquakes is very efficient for detecting small amplitude signals. The amplitude variation of the two phases will help us to know the characteristics of the seismic structure of the subducting slab.
DE: 7203 Body waves
DE: 7208 Mantle (1212, 1213, 8124)
DE: 7218 Lithosphere (1236)
DE: 7240 Subduction zones (1207, 1219, 1240)
DE: 8150 Plate boundary: general (3040)
SC: Tectonophysics [T]
MN: Fall Meeting 2005