Japan Geoscience Union Meeting 2014

Presentation information

Poster

Symbol S (Solid Earth Sciences) » S-EM Earth's Electromagnetism

[S-EM36_30PO1] Electrical conductivity, Tectono-electromagnetism

Wed. Apr 30, 2014 6:15 PM - 7:30 PM Poster (3F)

Convener:*Yamazaki Ken'ichi(Disaster Prevention Research Institute, Kyoto University), Noriko Tada(Japan Agency for Marine-Earth Science and Technology)

6:15 PM - 7:30 PM

[SEM36-P07] Conductivity structure beneath the fault segment gap in the Yamasaki fault zone, southwest Japan (2)

*Yusuke ODA1, Satoru YAMAGUCHI1, Hideki MURAKAMI2, Shigehiro KATOH3, Makoto UYESHIMA4, Toshiaki MISHIMA1, Yuhei OUCHI5 (1.Department of Geosciences, Graduate school of Science, Osaka City Univ., 2.Natural Sciences Cluster-Science Unit, Kochi Univ., 3.Division of Natural History, Hyogo Museum of Nature and Human Activities, 4.Earthquake Research Institute, The University of Tokyo, 5.Faculty of Science,Osaka City Universe)

Keywords:conductivity structure, active fault, Yamasaki fault system, Magnetotellurics

Abstract The Yamasaki fault zone (YFZ) of southwest Japan is a typical strike-slip fault system consisting of the Nagisen fault, the main strand of YFZ, and the Kusadani fault. The main strand of YFZ extends for over 79km and is divided into northwestern (NW) and southeastern (SE) groups based on their latest seismic activity. The NW group consists of the Ohara, Hijima, Yasutomi and Kuresaka-touge faults, and the SE group consists of the Biwako and Miki faults. The maximum magnitudes of the earthquakes generated by the NW and SE groups are estimated to be 7.7 and 7.3, respectively. Simultaneous activation of both fault groups is also pointed out to be as large as M = ~8.0 (The Headquarters for Earthquake Research Promotion, 2013). The subsurface structure beneath the fault segment gap between both groups will be the key information for assessing the possibility of such large earthquake. To infer the structure, we carried out Audio-frequency Magnetotelluric (AMT) survey at 11 sites along a transect between the NW group and the SE group and showed the two-dimensional resistivity model along the transect based on MT impedances. This model is characterized by three conductive zones. They locate beneath the points where the transect crosses the extension lines of the surface trace of the Yasutomi, Kuresaka-touge, and Biwako fault. We thus concluded that the Yasutomi and Kuresaka-touge faults are extended to southeast and the Biwako fault is extended to northwest further than the recognized terminals of their surface trace. In this presentation, we show the improved resistivity model which is determined by not only MT impedance but tipper vectors.