| 講演要旨(和文) | | 2011年3月11日の東北地方太平洋沖地震(M9.0)以降，福島県浜通りでは正断層型の地震が多数発生した．本震から1ヶ月後の4月11日にはM7.0の地震が発生し，従来知られていた活断層付近に正断層型の地震断層が出現した．活断層の地下構造の解明などを目標として，反射法と屈折法による地震探査を実施した．本報では反射法の中間結果を報告する．井戸沢断層の反射断面では，水平あるいは傾斜を持つ断続的なイベントが分布し，地震断層の位置を境にした東西の変化は顕著ではない．湯ノ岳断層の反射断面では，新第三系は北東に傾斜し，湯ノ岳断層付近を境とするハーフグラーベン状の堆積盆地を形成していると推定される．湯ノ岳断層の延長方の断面では，連続の良い複数の反射面が認められ，断層末端直近の反射断面で指摘されたような南西低下の反射面のずれは認められない． |
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| | 講演要旨(英文) | | Remarkable surface raptures appeared along Itozawa fault and Yunodake fault at the earthquake (M7.0) on April 11th, 2011, in Iwaki city, Fukushima prefecture. This earthquake is considered an induced earthquake of the 2011 off the Pacific coast of Tohoku earthquake (M9.0). We conducted seismic surveys along three lines which cross the Itozawa fault (line1) and Yunodake fault (line2) respectively and extension area of Yunodake fault (line3). The length of line1, 2, 3 are 6.6km, 6.5km and 4.2km, respectively. The seismic source was two - four Envirovibes. Source interval and receiver interval were 10m and two sweeps were stacked at one source point for the three lines. In line1 and 2, they were 5m within 1km from the surface raptures of the faults for high resolution survey and ten sweeps were stacked at 40m interval of source for deep reflection and refraction surveys. Many events are imaged but underground structures of faults are obscure in seismic sections of line1 and line2. Continuous reflectors are imaged and stratigraphic throws are not perceived on the whole seismic section of line3. |
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