Holocene Tsunami Traces on Kunashir Island, Kurile Subduction Zone

Abstract

The paper presents the detailed study of sediments deposited by middle-late Holocene tsunami in the Pacific Ocean at the Okhotsk Sea area and Izmena Bay coast of Kunashir Island. Seventeen thin sand-layers were found to be intercalated within peat of lacustrine deposits. Field data, grain-size composition, and biostratigraphical data allow interpretation of them as paleotsunami traces. Age of the sand-sheet was based on radiocarbon dating and tephrostratigraphy. Diatoms helped identify the tsunami deposits' origins and confirm that the sands had a marine source, and establish the landward extent of tsunami inundation. Tsunami deposits contain more contents of neritic and oceanic diatoms than marine units deposited during Holocene transgressions. The sand layers were deposited by tsunami with a maximal run-up more than 7 m, and penetration inland more the 2.5 km. The time period relating to the found tsunami deposits is 6,000–7,000 years. Correlation of tsunami events of Kunashir, Iturup Island, and Eastern Hokkaido have been done.