Trenching survey of the Sekiya fault in Tochigi Prefecture

Abstract

The Sekiya fault is an N-S-trending thrust in the northern part of Tochigi Prefecture. We surveyed the detailed geomorphic features of the Sekiya fault and opened three trenches on the northern part of the fault. The trenching survey has revealed that the last rupture event on the Sekiya fault occurred after the fall of the Haruna-Futatsudake-Ikaho Pumice in the 6th century. It is also made clear that a penultimate event occurred between ca. 5 ka and the 6th century.