反射法地震探査による房総半島南西部内房沿岸の浅部地下構造(<特集>首都直下地震防災・減災特別プロジェクトPart 3)

概要

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The southern part of the Boso Peninsula and its surroundings constitute one of the best regions for researching crustal movements causing disastrous earthquakes in the Tokyo metropolitan area, because records of crustal movements associated with these earthquakes are well preserved in Pleistocene trench slope sediments overlying Mio-Pliocene accretionary complexes. To reconstruct the last one million years of vertical crustal movements we performed a multi-channel seismic reflection survey called Boso 2008 in the inshore area off the southwestern part of the Boso Peninsula in September 2008. A 20-km-long seismic line was deployed from off Kanaya to Tateyama Bay in the N-S direction,and a 7-km-long seismic line was deployed in Tateyama bay in the E-W direction. Seismic data sets were obtained using an air-gun of 460cu. inch and a 300-m-long streamer cable with 24 channel hydrophones. Source and receiver spacings were 12.5m. The seismic data were processed by the common mid-point method and the seismic profile obtained clearly demonstrates the detailed geologic structure of the trench slope sediments of the Toyofusa Group. The two units, which correspond to the lower (1.0－0.7Ma) and upper (0.7－0.3Ma) Toyofusa Group, are identified on the seismic profile.
2010-03-29