Relationship between the upheaval process of the Uonuma Hills and the cumulative nature of the Muikamachi fault, central Japan

Abstract

This paper discusses the cumulative displacements and formation process of the Uonuma hills based on the geological cross sections and the dislocation of the fluvial terraces, central Japan. The Uonuma Hills has tilted to the west by the Muikamachi fault (NNW-SSE strike, length ca.30 km) at the eastern margin and the Suwatoge flexure (NNW-SSE strike, length ca.15 km) in the hills. Their active fault has the natures of the reverse fault of the west dip. The Uonuma Hills has uplifted with the uniform slip rate during the Quaternary by the Muikamachi fault. The slip rates are ca.1.0 m/ky at the north area and ca.2.0 m/ky at the south area of the Muikamachi fault. The longitudinal profile of the Uonuma Hills has the asymmetric form, which plunges from the south to the north, depending on the slip rate. Suwatoge flexure locates with the parallel to the Muikamachi fault in the northern area of the Uonuma Hills. The slip rate is ca.1.0 m/ky. Thus, the strains has been deposited and released with ca.2.0 m/ky slip rates, respectively, in the north and south areas of the Uonuma Hills.