Tectonic landforms associated with recent activities of the Minobu fault in the Fujikawa Valley and its implications, South Fossa Magna, Central Japan

Abstract

The Fujikawa Valley located at South Fossa Magna is filled by a thick sedimentary pile of Middle Miocene to Pleistocene age deformed by several large-scale faults. However, there is no report on the existence of active faults in the area between the Fujikawa-kako fault zone and Itoigawa-Shizuoka Tectonic Line active fault system. Based on aerial photograph interpretation and field observations, we find displaced landforms in the middle part of the Fujikawa Valley associated with the recent activities of the Minobu fault which has been identified as a pre-Quaternary fault by previous works. Geomorphic features such as systematically offset stream channels and scarps on terraces along the fault display that the Minobu fault is a left-lateral fault, trending NNW to SSE for a length of about 20 km. The horizontal slip rate during the late Pleistocene is more than 0.7 mm/yr. Our study suggests the Minobu fault, together with the Fujikawa-kako fault zone and the Itoigawa-Shizuoka Tectonic Line active fault system constitutes a major active tectonic zone in the western margin of the Fossa Magna.