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| | Abstract | | 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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