Subsurface structure of and rate of net slip on the Kamishiro fault, northern part of the Itoigawa-Shizuoka tectonic line, central Japan

概要

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The Kamishiro fault is one of the major active faults constituting the Itoigawa-Shizuoka Tectonic Line (ISTL) in central Japan. The Kamishiro fault is an east-dipping reverse fault. This fault cuts and warped the young lake deposits (late Pleistocene and Holocene in age) in the Kamishiro basin. The slip rate on the Kamishiro fault near the surface has been estimated by Geo-Slicer and shallow drillings survey, but was found to be significantly smaller than the vertical slip-rate that was estimated from the displacement of the AT volcanic ash. We carried out a 55 m deep drilling and a seismic reflection profiling using S-waves in this basin to clarify the subsurface structure of the Kamishiro fault. As a result, it was clarified that the Kamishiro fault is associated with drag folding near the surface. If we take the drag folding into account, the overall rate of slip on the fault would be as high as 4.4-5.2mmlyr during the past 28ka.
Japanese Society for Active Fault Studiesの論文