Three thousand year paleo-tsunami history of the southern part of the Japan Trench

Hokuto Higaki,Kazuhisa Goto,Daisuke Sugawara,Hideaki Yanagisawa,Takashi Ishizawa

doi:10.1186/s40645-021-00415-w

Abstract

This study conducted a field survey and multiproxy analyses on sediment cores retrieved from the Kobatake-ike pond in Choshi City, Chiba Prefecture, Japan. Kobatake-ike pond is located at a high elevation (i.e., 11 m above present-day sea level) and faces the southern part of the Japan Trench. Three event sand layers were detected within the continuous mud and peat sequences of 3000 years. Based on the multi-proxy analyses, including mineralogical composition, diatom assemblages, and geochemical markers, these sedimentological events were associated with past tsunamis. The most recent event was a sandy layer and is attributed to the AD 1677 Enpo tsunami, which was reported by an earlier study conducted in the pond. Our results demonstrated that two older sand layers are associated with large tsunamis that struck the Choshi area in AD 896–1445 and in BC 488–AD 215. In addition, the age ranges of these events seem to overlap that of large earthquakes and tsunamis known from the central part of the Japan Trench. This implies a possible spatiotemporal relation of earthquake generations between the central and southern parts of the Japan Trench. However, since the error ranges of the ages of tsunami deposits at the southern and central parts of the Japan Trench are still large, further investigation is required to clarify the relations of large earthquakes in both areas.

Highlights

The Tohoku-oki earthquake and tsunami on March 11, 2011 caused severe damage to the Pacific coast from Tohoku to the Kanto region (Toda 2012)
Considering the geomorphological, sedimentological, and mineralogical evidences together with supportive paleontological and geochemical evidences, we identified the deposits of events 1–3 as tsunami deposits and the sediment source of them as the beach sand at Kimiga-hama
5.6 Paleotsunami history along the southern and central part of Japan Trench Our results demonstrated that three massive tsunamis struck the studied area during the past 3000 years: AD 1677, AD 896–1445, and BC 488–AD 215

Summary

Introduction

The Tohoku-oki earthquake and tsunami on March 11, 2011 caused severe damage to the Pacific coast from Tohoku to the Kanto region (Toda 2012). Seismological studies by Simons et al (2011) and Toda et al (2011) reported that the strain balance has changed in the southern part of the Japan Trench due to the earthquake. The studies indicated the possibility of an increase in the risk of future occurrence of large earthquakes in this region. Historical records and tsunami deposits need to be investigated to understand the recurrence interval and magnitudes of large earthquakes in this region and risk assessment. Tsunami deposits are useful for identifying tsunami events with more extended time scales, i.e., more than hundreds of years. They are effective for detecting huge tsunami events with prolonged recurrence

Results

Discussion

Conclusion