The current situation of tsunami geology under new policies for disaster countermeasures in Japan

Abstract

This paper presents a review of the Japanese policies for tsunami countermeasures before and after the 2011 off the Pacific coast of Tohoku Earthquake and its consequent tsunami. The current status of tsunami geology under the new policies is also discussed. The 2011 event was regarded as an unexpected hazard. Such a large hazard had not been considered for Japanese tsunami countermeasures before, although geological studies have indicated their potential occurrence. Based on lessons learned from the 2011 event, the Japanese government changed policies related to tsunami disaster countermeasures. The salient change is that estimation of the maximum possible earthquake and tsunami along the each coast of Japan is now required. Following this policy change, the maximum possible earthquake and tsunami have been estimated along several coasts of Japan, such as the Nankai Trough region based on seismology, irrespective of past occurrence. Tsunami geology is regarded as an important research field for estimating the maximum possible earthquake and tsunami strength because paleotsunami histories of several thousand years are crucially important for future tsunami risk assessment. However, many issues remain to be resolved to respond to the rapid change of policy. Acceleration of studies, sharing knowledge with governors, and development of schemes for outreach to the public (e.g. a database system) should be considered for improvement of future tsunami countermeasures in Japan.