| 講演要旨(和文) | | 東北地方太平洋沖地震(2011.3.11)の１ヶ月後(2011.4.11)に起った福島県浜通りの地震に伴い，福島県いわき市の南東部において既知の活断層である井戸沢断層と湯ノ岳・藤原断層付近に沿って顕著な地震断層が出現した。特に，長さ約15kmにわたり断層が現れた湯ノ岳・藤原断層に近い温泉街では，地震の前後で温泉の湧水量に極端な変化があったと報告されている。深度1kmまでの地下構造を調査することを目的に，NW-SE方向の同断層南端部に6測線を設置したCSAMT法探査を行った。2次元解析はTMモードの見掛比抵抗データを使って行った。その結果，2次元解析断面には断層を境に横方向の比抵抗の相違が認められた。すなわち，断層の北東側に高比抵抗部（10〜100Ωm），南西側に低比抵抗部（2〜10Ωm）が捉えられた。一方，地震断層が認められなかった最南端の測線では，横方向の比抵抗変化は不明瞭となった。 |
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| | 講演要旨(英文) | | Remarkable surface raptures appeared along the Yunodake-Fujiwara Fault in Iwaki City, Fukushima Prefecture, is estimated to be generated with an earthquake (Mw 6.6) on April 11, 2011 in southeastern Fukushima Prefecture, which occurred one month after the Great East Japan Earthquake (Mw 9.0) on March 11, 2011. We conducted a CSAMT survey to investigate the underground structure of a southern end part of the fault. Six survey lines were arranged perpendicular to the fault's direction (NW-SE), and the transmitter current source, with a 2km length, was set at about 5 km southeastward from the survey area. A 2D inversion was carried out for each survey line using TM-mode apparent resistivity data. As a result, lateral resistivity changes were clearly recognized in the 2D resistivity sections at the locations of the fault. High resistivity zones (10-100ohmm) were detected in the northeast side of the fault, while low resistivity zones (2-10ohmm) were located at the southwest side. On the other hand, a lateral resistivity change was not detected clearly on the southeastern most survey line, where the earthquake fault was not confirmed on the ground surface. |
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