Tectonic movement and landform development along the eastern margin of the Fukui plain

Abstract

The Fukui plain is located near the Japan Sea coast in central Japan. Fluvial terraces composed of late Pleistocene and Holocene sediments are distributed along the eastern margin of the plain. Late Pleistocene marine terraces are located on the Kaetsu uplands, which are located in the northern part of the Fukui plain. These terraces are tephrostratigraphically and height-distributively divided into the M 1 surface, M 2 surface, M 3 surface, Mf surface, Lf 1 surface, Lf 2 surface, and Lf 3 surface in descending order. Active faults striking nearly in the north-south direction extend along the eastern margin of the plain. These faults tend to show an eastside uplift. One of the faults along the boundary between the hills and the plain has only a vertical slip. The other fault separates mountains and hills and has a sinistral slip. Those faults displaced Lf1 and Lf2 fluvial terrace surfaces, and the vertical slip rates of these faults (estimated from topographic profiling and the age of terraces) are 0.1-0.3 m/ky. There was a severe earthquake (Fukui earthquake) in the Fukui plain in 1948. Although geodetic data on the earthquake fault of the Fukui earthquake had a 2m sinistral slip across the plain in the NNW-SSE direction, surface ruptures did not appear distinctly. The reason is considered to be because the Fukui earthquake fault runs in the alluvial plain and the soft sediments might have absorbed the displacement in it. In the Fukui plain, the basal topography of the Quaternary deposits indicates deformation with different patterns on both sides of the Fukui earthquake fault. This deformation caused an uplift of the southeastern part of the Kaetsu uplands and depressed the structure of the basement in the northern part of the Fukui plain. The topography of the eastern part of the Fukui plain was formed as a result of the cumulative activity of the eastern marginal faults and the Fukui earthquake fault.