箱根地震活動域周辺でのAMT観測 : 序報

Abstract

2011年3月11日の東北地方太平洋沖地震の発生を受けて，誘発的地震活動の活発化の見られた箱根火山地域において，その発生域の構造的特徴を把握するために，2011年12月に計39観測点でのAudio-frequency Magnetotelluric (AMT) 法探査を実施した。既存の広帯域MT法探査のデータも加え，位相テンソル楕円・インダクションベクトルを各周期で求めたところ，駒ヶ岳直下ならびに金時山南方に良導体の存在を示唆する結果が得られた。この領域は，東北地方太平洋沖地震に即時応答して活動度が高まった場所に対応する。

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. As the result of remote-reference processing using local sites, we obtained fair sounding curves at most sites for frequencies higher than 1Hz. The spatial distribution of the induction vectors and the phase tensor ellipses suggests that conductive bodies may lie beneath the remarkable regions in which the seismicity increased abruptly just after the occurrence of the Tohoku Earthquake.