HR: 15:20h
AN: S33D-07    [Abstracts]
TI: Shear-wave splitting analysis at the Niigata-Kobe Tectonic Zone using the seismic network of the Joint Seismic Observations at NKTZ
AU: * Iidaka, T
EM: iidaka@eri.u-tokyo.ac.jp
AF: Earthquake Research Institute, Univ. of Tokyo, Yayoi 1-1-1, Bunkyo, Tokyo, 113-0032, Japan
AU: Hiramatsu, Y
EM: yoshizo@hakusan.s.kanazawa-u.ac.jp
AF: Kanazawa University, Kakuma-machi, Kanazawa, 920-1192, Japan
AU: Iwatsuki, K
EM: iwtk-kou@hakusan.s.kanazawa-u.ac.jp
AF: Kanazawa University, Kakuma-machi, Kanazawa, 920-1192, Japan
AU: Ueyama, S
EM: ueyama@hakusan.s.kanazawa-u.ac.jp
AF: Kanazawa University, Kakuma-machi, Kanazawa, 920-1192, Japan
AU: the Joint Seismic Observations at NKTZ, J
EM: iidaka@eri.u-tokyo.ac.jp
AF: Japanese University Group of the Joint Seismic Observations at NKTZ, Yayoi 1-1-1, Bunkyo, Tokyo, 113-0032, Japan
AB: In central Japan, high strain rate zone which was called Niigata-Kobe Tectonic zone (NKTZ) was detected by GPS study. Many historical large earthquakes have occurred inside the NKTZ. A large right lateral Atotsugawa fault is located in NKTZ. The understanding of the cause of NKTZ will be important to know the accumulation mechanism of the stress and strain in Japan. It is well known that elastic anisotropy of the earth is closely related to mantle dynamics. The studies of shear-wave splitting will be important to know the mantle dynamics beneath NKTZ. We conducted seismic observation at the area with a spatially high dense seismic array. The seismic network was used for the analysis of shear-wave splitting to detect the heterogeneous structure at the crust and upper mantle at NKTZ. The deep earthquakes with depth of deeper than 280 km are used. The deep earthquakes are located beneath the seismic network. The large lateral variation was found on the polarization direction in the results of our study. The research area was divided into 4 regions based on the observed polarization directions. One is the northern part of the research area. In this area, the polarization direction was NW-SE. The eastern part of this research area indicated NE-SW directions. In the central part of the research area, the polarization direction was NNE-SSW. The E-W polarization direction was obtained at the seismic stations located in the southern part of the research area. The large shear-wave splitting, which is larger than 0.6 sec on time lag data, could not be explained by the crustal anisotropy. The cause of the shear-wave splitting should be located in the mantle wedge. Lack of the spatially distribution of the seismic stations prevents high resolution study in this area. Recently, seismic tomography studies using spatially high dense seismic network indicated high resolution velocity structure in this area. The configuration of the subducting Philippine Sea slab was clearly delineated. The observed polarization directions are consistent with the subduction direction of Philippine Sea slab. The observed shear-wave splitting can be explained by the preferred orientation of the olivine crystal which was caused by the mantle flow.
DE: 7200 SEISMOLOGY
DE: 7203 Body waves
DE: 7208 Mantle (1212, 1213, 8124)
DE: 7240 Subduction zones (1207, 1219, 1240)
SC: Seismology [S]
MN: 2007 Fall Meeting