Identifying storm surge deposits in the muddy intertidal zone of Ena Bay, Central Japan

Abstract

Storm surge and tsunamis deposits provide essential information for those tasked with mitigating the impacts of natural disasters on coastal lowlands in low- and middle-latitude regions and also along active margins. However, studying these deposits in coastal lowland strata is becoming increasingly difficult, particularly in residential regions, because of extensive anthropogenic disturbance. Researchers have therefore had to extend the scope of their work to include shallow marine deposits such as bay sediments, and some have also worked on storm surge deposits related to recent storm events. In this study, we identified and examined sandy storm surge deposits of up to 14 cm thick that were deposited by 2017 Typhoon Lan (lowest pressure of 915 hPa), the largest storm in the past 60 years, within the tidal flat sediments of Ena bay, in the southern coastal area of metropolitan Tokyo, Central Japan. We compared these deposits with the tsunami deposits (10–50 cm thick) found on the tidal flats of Koajiro Bay, near Ena Bay, that resulted from the Kanto earthquake (magnitude ~8). These differences mean that the thickness of such deposits is a valid criterion for distinguishing between storm surge and tsunami deposits on tidal flats.