HR: 17:30h
AN: GP12B-07    [PDF]
TI: The 1998 M5.0 Main Shock Region in Sendai, Japan, Imaged by magnetotellurics
AU: * Ogawa, Y
EM: oga@ksvo.titech.ac.jp
AF: Volcanic fluid research center,Tokyo Institute of technology, 2-12-1 Ookayama, Meguro, Tokyo, 152-8551 Japan
AU: Mishina, M
AF: Research Center for Prediction of Earthquakes and Volcanic Eruptions Graduate School of Science, Tohoku University, Aoba-ku, Sendai, 980-8578 Japan
AU: Honkura, Y
AF: Department of Earth and Planetary Sciences,Tokyo Institute of technology, 2-12-1 Ookayama, Meguro, Tokyo, 152-8551 Japan
AU: Takahashi, K
AF: Research Center for Prediction of Earthquakes and Volcanic Eruptions Graduate School of Science, Tohoku University, Aoba-ku, Sendai, 980-8578 Japan
AU: Tank, S B
AF: Volcanic fluid research center,Tokyo Institute of technology, 2-12-1 Ookayama, Meguro, Tokyo, 152-8551 Japan
AU: Tank, S B
AF: Department of Earth and Planetary Sciences,Tokyo Institute of technology, 2-12-1 Ookayama, Meguro, Tokyo, 152-8551 Japan
AB: We imaged the resistivity structure of the 1998 M5.0 Earthquake Sendai which was located at 10--12km depth at the deep extension of the active Nagamachi-Rifu Fault. We had 63 magnetotelluric stations mostly along three profiles perpendicular to the fault trace. The magnetotelluric data showed strong two-dimensionality in the period range between 1s to 1000s. The estimated regional strike is consistent with the tectonic stress field and the surface trace of the fault. We used tensor--decomposed apparent resistivity and phase in two modes and projected magnetic transfer functions for two-dimensional inversions in 1s-1000s period. The final models showed the main shock regions as a resistive gap in between the mid--crustal conductors. One of the conductors is located at the deep extension of the fault, which is also characterized by the seismic low velocity and high Vp/Vs ratio. This implies the distribution of fluids at the root of the active fault, which may help accommodate the quasi--stationary preslip before the main shock.
DE: 0925 Magnetic and electrical methods
DE: 1515 Geomagnetic induction
DE: 7209 Earthquake dynamics and mechanics
DE: 8015 Local crustal structure
DE: 8123 Dynamics, seismotectonics
SC: Geomagnetism and Paleomagnetism [GP]
MN: 2003 Fall Meeting