著者

岡村 行信

出版者

一般社団法人 日本活断層学会

雑誌

活断層研究 (ISSN:09181024)

巻号頁・発行日

vol.2010, no.33, pp.15-25, 2010

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Geologic structure around the source area of the 2007 Chuetsu-oki earthquake and the Sado Basin was examined based on seismic profiles. The earthquake occurred in the fold belt of the Niigata basin, one of the largest Miocene rift basins in Japan. High-resolution multi-channel seismic profiles in and around the source area showed that there are active folds and inactive folds. One of the NE-SW trending active folds has been related to the SE dipping source fault of the 2007 earthquake, which continues from the shelf to the basin. The fold is parallel to the strike of the source fault of the 2007 earthquake, but is located about 5 km northwest of the source area. Other folds above and around the source area of the 2007 Chuetsu-oki earthquake are inactive. The active anticline accompanies 5 m vertical offset on the erosional surface during the last glacial age and the surface sediments covering the Sado Basin. The active anticline does not continue to the north of 37°38′N. The slope of the SE side of the Sado Basin is underlain by nearly horizontal sediments and the slope has been developed by progradation of shelf slope during glacial ages. These observations on seismic profiles indicated that the active fault and anticline related to the 2007 Chuetsu-oki earthquake does not extend to the northeast along the southeastern slope of the Sado Basin except in the southern most part.