Earth Planets Space, Vol. 54 (No. 5), pp. 629-636, 2002
Yukio Fujinawa1, Noriaki Kawakami2, Jun Inoue2, Theodore H. Asch2, and Shinji Takasugi3
1National Research Institute for Earth Science and Disaster Prevention, Tennohdai 3-1, Tsukuba-shi, Ibaraki 305-0006, Japan
2Geothermal Energy Research and Development Co., Ltd., 11-7, Kabuto-cho, Nihonbashi, Chuo-ku, Tokyo 103-0026, Japan
3Geothermal Engineering Co., Ltd., 804, Koami-cho, Nihonbashi, Chuo-ku, Tokyo 103-0016, Japan
(Received January 22, 2001; Revised December 27, 2001; Accepted January 14, 2002)
Abstract: Wideband magnetotelluric (MT) observation data were obtained from 91 sites along six transects in the central part of the Japan Arc. Here, a quasi-3D georesistivity distribution, in addition to other geophysical and geological parameters, is used to better understand seismicity in the region. We found that high seismicity in the Central Mountain Range is due to relatively poor fluid saturation caused by volcanism. The high conductive fracture zone in the west of the Central Basin without big earthquakes is characterized by a low Poisson ratio. It is suggested that strains cannot be accumulated in those regions. The Miyagi-ken-hokubu region with a frequent occurrence of large earthquakes, is conductivehigh Poisson ratiohigh Vp suggesting that the zone is relatively fluid-rich and brittle.