2002 Volume 2002 Issue 22 Pages 45-54
An active reverse fault zone, about 50 km long trending NW-SE, that is known by having caused the Zenkoji earthquake in 1847, exists at the northwestern boundary of Nagano basin, central Japan and the southwestern part of this fault zone, is named Komatsubara fault. As the result of precise air-photo interpretation of tectonic landforms, surface rupture traces which occurred during the 1847 Zenkoji earthquake were found along the Kamatsubara fault. The traces consist of east-facing small and fresh flexure scarps on lower terrace and alluvial plain and extend for about 3 km at least. Such evidence indicates that the Kamatsubara fault thrust up toward the east in 1874, and then the ground surface was displaced 2 m or more in vertical. In this area, we can recognize too flexure scarps formed by the fault event just before the 1847 Zenkoji earthquake.
