著者

井上 卓彦 村上 文敏 岡村 行信 池原 研

出版者

地震研究所

雑誌

東京大学地震研究所彙報 (ISSN:00408972)

巻号頁・発行日

vol.82, no.4, pp.301-312, 2007

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The 2007 Noto Hanto Earthquake (MJMA 6.9) occurred on 25 March, 2007 at 37°13.2′N, 136°41.1′E, under the northwestern coast of Noto Peninsula, Ishikawa Prefecture. To clarify distribution and activity of active fault, a high-resolution multi-channel seismic survey was carried out in the source area using Boomer and a 12 channel streamer cable. Seismic profiles depict geologic structure up to 150 meters deep under sea floor. Sedimentary sequences ranging in age from Miocene to Holocene time are deformed by ENE-WSW to N-S trending folds and faults. The deformed sediments were truncated by erosional surfaces. The age of erosion is not clear in the offshore area, but the most remarkable erosion surface was formed at the Last Glacial Maximum (LGM) age. The surface is covered by Holocene sediments up to 40m thick. A NW downthrown fault continues in the ENE-WSW direction for more than 21 kilometers. The fault cuts Neogene sediments, but the deformation in the Holocene sediments is recognized as flexure. The fault is located near the northern margin of the aftershock area of the 2007 earthquake, supporting that the fault is connected to the source fault of the 2007 earthquake. The deformations in the Holocene sediments increase downward, indicating that the fault slipped repeatedly during the period of Holocene time. Comparison between the 3.5kHz SBP profiles obtained in 1988 and twelve channel seismic profiles after the earthquake suggests that the deformation during the 2007 earthquake occurred on the seafloor along the fault.