A 17th-century Tsunami Deposit Discovered on the Eastern Iburi Coast, Hokkaido, Northern Japan

Abstract

A characteristic sandy layer probably resulting from a 17th-century tsunami was discovered in coastal sediments in the central part of the Pacific coast (eastern Iburi coast) of Hokkaido, northern Japan. The sandy layer was identified as of tsunami origin based on the following characteristics. The deposit is 1) distributed at least 20km long and 1-2km wide along the coast ; 2) widely inundated along the river toward the inland ; 3) deposited approximately eight meters at the highest ; 4) shows a fining- and thinning- landward trend, and 5) yields a marine diatom assemblage.
The sandy layer was deposited in the early to mid 1600s. The exact trigger event of this tsunami was not identified in this study. Great subduction-zone earthquake centered off eastern Hokkaido and the 1640 Hokkaido Komagatake eruption are candidate source events for this tsunami.