Sedimentological study of postulated tsunami deposits along the Kuril subduction zone, eastern Hokkaido, northern Japan: preliminary study around the Kiritappu marsh land

Authors: Futoshi Nanayama, Kenji Satake, Koichi Shimokawa, Kiyoyuki Shigeno(Niigata Univ.) and Ryuta Furukawa

Index Map

Abstract:Large earthquakes in the Kuril subduction zone have caused tsunami damage along the Pacific coast of eastern Hokkaido, between Nemuro and Tokachi coast, northern Japan. In a preliminary study of postulated tsunami deposits, seven postulated tsunami sand layers (named Ts1 to Ts7 in descending order) have been found in a peat layer around the Kiritappu marsh land by sedimentological, tephrochronological and micropaleontological methods. Ts7, Ts6 and Ts5 are under a regional tephra B-Tm, which is dated as ca. 9th century. Ts4 is dated 9th to 13th century, and Ts3 is 13th to 17th century. Ts3 may correspond to a tsunami event documented in historical records, and it may have been the biggest tsunami event judging from its wide distribution and thick sand layer along the eastern coast of Hokkaido. Ts2 and Ts1, which are above a regional tephra layer Ta-a of ca. 1739 AD, are dated 19th and 20th century, respectively.