[S-SS31_30PM1] 内陸地震への包括的アプローチ

[SSS31-03] 箱根火山周辺の比抵抗構造と東北地方太平洋沖地震に誘発された地震活動の関係

*吉村 令慧¹、小川 康雄²、行竹 洋平³、神田 径²、小森 省吾⁴、後藤 忠徳⁵、本多 亮³、原田 昌武³、山崎 友也¹、加茂 正人¹、安田 陽二郎⁶、谷 昌憲⁵ (1.京都大学防災研究所、2.東京工業大学火山流体研究センター、3.神奈川県温泉地学研究所、4.中央研究院地球科學研究所、5.京都大学大学院工学研究科、6.鳥取大学大学院工学研究科)

キーワード：MT法探査, 3次元比抵抗構造, 箱根火山, 誘発地震

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.