Japan Geoscience Union Meeting 2016

Presentation information


Symbol S (Solid Earth Sciences) » S-CG Complex & General

[S-CG63] Dynamics in mobile belts

Mon. May 23, 2016 5:15 PM - 6:30 PM Poster Hall (International Exhibition Hall HALL6)

Convener:*Yukitoshi Fukahata(Disaster Prevention Research Institute, Kyoto University), Norio Shigematsu(Research Institute of Earthquake and Volcano Geology, Geological Survey of Japan, National Institute of Advanced Industrial Science and Technology), Aitaro Kato(Graduate School of Environmental Studies, Nagoya University), Hikaru Iwamori(Geochemical Evolution Research Program, Japan Agency for Marine-Earth Science and Technology), Yasutaka Ikeda(Department of Earth and Planetary Science, Graduate School of Science, University of Tokyo), Toru Takeshita(Department of Natural History Sciences, Graduate School of Science, Hokkaido University)

5:15 PM - 6:30 PM

[SCG63-P10] Resistivity structure of Beppu-Haneyama fault zone

*Koki Aizawa1, Takao Koyama2, Azusa Shito1, Asuma Wakabayashi4, Masahiro Miyazaki3, Kazunari Uchida1, Yuko Tsukashima1, Kaori Tsukamoto4, Kanade Takashima1, Kentaro Kondo1, Hiroki Kawamoto4, Shiori Fujita1, Yuto Yamamoto4, Miki Ogata4, Makoto Uyeshima2 (1.Institute of Seismology and Volcanology, Faculty of Sciences, Kyushu University, 2.Earthquake Research Institute, University of Tokyo, 3.Disaster Prevention Institute, kyoto university, 4.Department of Earth and Planetary Sciences, Faculty of Sciences, Kyushu University)

Keywords:Magnetotellurics, Resistivity structure, Earthquake swarm

By using the broad-band magnetotelluric (MT) data acquisition system (Metronix ADU-07 system) and the recently developed telluric loggers (NT System Design ELOG1K), we measured electromagnetic fields in the eastern part of the Beppu-Haneyama fault zone, Kyushu island, Japan. At 53 telluric measurement sites, the MT impedances were calculated by using the magnetic fields recorded at other sites. Total number of Broad-band (200~0.0003 Hz) MT and telluric sites amounted up 73. Preliminary 3-D inversion shows the following features of the resistivity structure; (1) sub-vertical conductors are imaged at a shallow level beneath the faults; (2) the deep resistivity structure is approximately trending NE-SW direction that is not consistent with the EW-trending directions of the fault zone. The studied area is known not only as the faults but also as geothermal activities with famous hot-springs (Beppu and Yufuin) and three active volcanoes (Tsurumi, Garan, and Yufu). Therefore, it is likely that the geothermal fluids supplied beneath the volcanoes flows along NE trending faults, then discharges out in hot springs. However, the preliminary result shows that the deep trend of the resistivity structure is not consistent with the surface trace of faults, which may imply the faults are not extended to the deep level. It should be noticed that the hypocenters of earthquake swarms around Beppu City in 2007 (Maeda et al., 2010) are distributed NE-SW horizontally, which is consistent with the trend of deep resistivity structure. This may suggest that the fluids movement was not guided by the faults but by the deep resistivity structure, subsequently triggered the earthquake swarms in around Beppu City.
We are greatly indebted to the land owners for their permission for field campaigns. The MT data were partly obtained using the ADU07 system from Earthquake Research Institute, University of Tokyo (Kyodo-Riyo Code 2015-F2-04). The geomagnetic data used for the remote-reference processing were provided by the Kakioka Geomagnetic Observatory of JMA. Our gratitude goes to Y. Ogawa and W. Siripunvaraporn for supplying his 2-D and 3-D inversion code. We used the computer systems at the Earthquake Information Center of the Earthquake Research Institute, University of Tokyo, for 3-D inversion of the resistivity structure. This study was supported by the Ministry of Education, Culture, Sports, Science and Technology (MEXT) of Japan.