[S-SS31_30PM1] Comprehensive approach to the intraplate earthquakes

[SSS31-03] Relation between the resistivity structure around Hakone volcano and seismicity induced by the 2011 Tohoku Earthquake

*Ryokei YOSHIMURA¹, Yasuo OGAWA², Yohei YUKUTAKE³, Wataru KANDA², Shogo KOMORI⁴, Tada-nori GOTO⁵, Ryou HONDA³, Masatake HARADA³, Tomoya YAMAZAKI¹, Masato KAMO¹, Yojiro YASUDA⁶, Masanori TANI⁵ (1.DPRI, Kyoto University, 2.Volcanic Fluid Research Center, Tokyo Institute of Technology, 3.Hot Springs Research Institute of Kanagawa Prefecture, 4.Institute of Earth Sciences, Academia Sinica, 5.Graduate School of Engineering, Kyoto University, 6.Graduate School of Engineering, Tottori University)

Keywords:magnetotellurics, three-dimensional resistivity structure, Hakone volcano, triggered earthquake

Seismicity around the Hakone volcano was activated just after the arrival of surface waves caused by the 2011 off the Pacific coast of Tohoku Earthquake. Most of these triggered earthquakes had similar distribution to prior occasional swarm activities. In order to image electrical properties around such seismic events, we carried out audio-frequency magnetotelluric (AMT) measurements at 39 sites in December 2011 (Yoshimura et al., 2012). In this study, we conducted 3D modeling of dense AMT (Yoshimura et al., 2012) and MT (Ogawa et al., 2012) data, to figure out electrical characteristics around the triggered seismicity. In spite of careful treatments for noise reduction, the effects of noise were still seen on the longer parts of the responses (< 1 Hz) at the several measurement sites. Thus we determined to have use of the frequency range from 320 Hz to 1.02 Hz. The full components the impedance tensors at 51 sites in total were inverted using the code developed by Siripunvaraporn et al. [2005]. The model space consists of 64(x-)×46(y-)×36(z-direction; including 7 air layers) blocks. The minimum horizontal size of blocks was 400m×400m. Significant characteristics of the obtained three-dimensional resistivity model are: (1) the most of the triggered earthquakes, which occurred shallower than a depth of 4km, seem to align along edges or areas just inside the relatively resistive block; (2) surface conductive blocks, in which there were very few earthquakes, were observed beneath not only fumarolic areas but geothermal non-active regions.