Large Earthquakes Recorded as Deep-sea Turbidites in the Rishiri Trough, Northernmost Hokkaido.

Abstract

Two turbidite layers of earthquake origin were found in a sediment core collected from the Rishiri Trough, west of Rebun Island, northernmost part of Hokkaido, Japan. Radiocarbon age determinations using planktonic foraminiferal tests in hemipelagic mud indicated that the depositional ages of each turbidite were 2,300 C-14 yrs BP and 5,500 C-14 yrs BP, respectively. Therefore, the recurrence interval of the large earthquakes forming the turbidites in this area was estimated to be around 3,200 years. This interval is longer than that around the Okushiri Ridge (around 1,000 years), wes of Hokkaido near the hypocenter of the 1993 Hokkaido-nansei-oki Earthquake, or that in northern Sakhalin (more than 2,000 years).