HR: 1330h
AN: G43B-08    [Abstracts]
TI: Spatial Variation on a Direction of Maximum Horizontal Compression in and around the Atotsugawa Fault System, Japan, Inferred from Shear Wave Splitting
AU: * Mizuno, T
EM: takashi.mizuno@aist.go.jp
AF: Geological Survey of Japan, AIST, Japan, Central 7, Higashi 1-1-1, Tsukuba, Ibaraki, 3050044 Japan
AU: Kuwahara, Y
AF: Geological Survey of Japan, AIST, Japan, Central 7, Higashi 1-1-1, Tsukuba, Ibaraki, 3050044 Japan
AU: Ito, H
AF: Geological Survey of Japan, AIST, Japan, Central 7, Higashi 1-1-1, Tsukuba, Ibaraki, 3050044 Japan
AU: Imanishi, K
AF: Geological Survey of Japan, AIST, Japan, Central 7, Higashi 1-1-1, Tsukuba, Ibaraki, 3050044 Japan
AU: Takeda, T
AF: Geological Survey of Japan, AIST, Japan, Central 7, Higashi 1-1-1, Tsukuba, Ibaraki, 3050044 Japan
AB: We investigated a shear wave splitting of micro earthquakes occurred in and around the Atotsugawa fault system, Central Japan, to infer a spatial variation of the direction of maximum horizontal compression (Shmax). Leading shear wave polarization directions (LSPD) indicate that the maximum compressional axis trends WNW-ESE, which is nearly consistent with the direction of the regional Shmax inferred from geodetic observations and focal plane solutions of micro earthquakes. In addition, we find a spatial varation on a direction of Shmax along and across the fault. The angle between the direction of Shmax and the fault strike ( φ ) ranges 20 - 40 degrees for the most of stations at the eastern part of the fault, and 40 - 45 degrees at the central part of the fault. Moreover φ changes across the central part of the fault. Whereas φ ranges 55 - 70 degrees to the fault strike at the stations away from the fault, φ takes 40 - 45 degrees at the vicinity of the fault. In order to clarify the main cause of the spatial variation of the direction of Shmax across and along the fault, we performed a finite element modeling of the stress field in and around the Atotsugawa fault. Since the displacement field has been investigated by GPS observation at the central part of the Atosugawa fault, we incorporated it into a boundary condition of model space. Although the maximum stress direction at the central part of the Atotsugawa fault can be reproduced with the stable sliding at the deep extension of the fault, the direction of Shmax at the eastern part of the Atotsugawa fault cannot be explained by any possible models. Improving a boundary condition of the eastern part of the Atotsugawa fault or incorporating internal forces at the eastern part of the Atotsugawa fault is necessary to perform more sophisticated modeling on the variation of the direction of Shmax for the Atotsugawa fault area.
UR: http://staff.aist.go.jp/takashi.mizuno/
DE: 7205 Continental crust (1242)
DE: 7209 Earthquake dynamics and mechanics
DE: 8015 Local crustal structure
DE: 8123 Dynamics, seismotectonics
DE: 8164 Stresses--crust and lithosphere
SC: Geodesy [G]
MN: 2005 Joint Assembly