HR: 0800h
AN: GP41B-0870    [Abstracts]
TI: A Magnetotelluric Investigation Across the Western Aizu Basin Active Fault Zone, Northeast Japan
AU: * Takakura, S
EM: takakura-s@aist.go.jp
AF: Institute for Geo-Resources and Environment, GSJ, AIST, Tsukuba Central 7, 1-1-1 Higashi, Tsukuba, 305-8567 Japan
AU: Yamamoto, T
EM: t-yamamoto@aist.go.jp
AF: Research Center for Deep Geological Environments, GSJ, AIST, Tsukuba Central 7, 1-1-1 Higashi, Tsukuba, 305-8567 Japan
AU: Takeno, N
EM: n.takeno@aist.go.jp
AF: Research Center for Deep Geological Environments, GSJ, AIST, Tsukuba Central 7, 1-1-1 Higashi, Tsukuba, 305-8567 Japan
AB: The western Aizu basin active fault zone in northeast Japan consists of some north-striking reverse faults. The position of the newest earthquake fault is greatly separated with the main faults. From the seismic survey that was conducted across the active fault zone, it was thought that the faulting moved to the east 5 km from the main faults after entering the Quaternary. In order to investigate the deep geological structure and estimate the distribution of fluids, clay minerals and concealed faults at depths around the fault zone, magnetotelluric (MT) measurements were carried out at 28 sites, which were located on a 29 km-long profile along the seismic survey line. A resistivity model obtained from 2D inversion of the MT data shows subsurface specific conductive and resistive features around the fault zone. Resistive layers at or near surface correspond to Quaternary sediments which were not altered. Below them, thick conductive layers that correspond to Tertiary sediment rocks are present. The low resistivity is probably due to water-bearing clay minerals produced by diagenesis or hydrothermal alteration. Deep resistive layers may correspond to intrusive and the pre-Tertiary sedimentary rocks that are the basement of the Aizu basin. There are some discontinuous parts in the conductive layers, indicating the Tertiary sedimentary rocks are cut by faults. Although the west side of the faults was uplifted, the bottom of the conductive layers (Tertiary sedimentary rocks) is deeper on the west side of the faults than on the east. It seems that the faults were originally normal but are now inverted by a change of stress field in this area.
DE: 3914 Electrical properties
DE: 5109 Magnetic and electrical properties (0925)
DE: 8004 Dynamics and mechanics of faulting (8118)
SC: Geomagnetism and Paleomagnetism [GP]
MN: Fall Meeting 2005