Activity of the Atera fault based on analysis of outcrops on the left bank of the Kiso River, Yamaguchi Village, Nagano Prefecture, central Japan

Abstract

The 70-km-long Atera fault system is composed of several fault segments with mainly left-lateral strikeslip displacement in the eastern part of southwest Japan. The Atera fault is the longest segment in this fault system. We investigated geomorphology and geology around a fault outcrop on the left bank of Kiso River, Yamaguchi Village, Nagano Prefecture. Vertical displacements of Kiso-gawa volcanic mudflow deposit, M2surface, and the deposit of L 1 surface are 15.4m,13.0m., and 8.5m, respectively. Vertical slip rate of the Atera fault is 0.3-0.4mm/yr in the study area.