The active fault related to the 2008 Iwate-Miyagi Nairiku Earthquake in Japan

Preliminary report of the earthquake fault in Genbi-cho, Ichinoseki city

Abstract

Since the 2008 Iwate-Miyagi Nairiku Earthquake occurred in the area where detailed active fault studies had not been done before, it is important to define whether the earthquake is related to any existing active fault or inactive fault. We interpret large-scale aerial photographs taken in 1976 as well as taken immediately after the earthquake, in order to compare well-defined surface fault ruptures with pre-existing fault-related landform sporadically distributed along the Koino'oka river in Genbi-cho, Ichinoseki city. In the field, we confirmed that these surface ruptures and deformation partially appeared along the pre-existing fault-related landform. Further, we excavated trenches across the earthquake fault, and found that the fault has been repeatedly moved during Holocene. Thus we confirmed that the cause of the earthquake was strongly related to this newly found active fault.