Paleoseismology from deep-sea turbidites in the lower Kuril Slope, offshore east Hokkaido

Deep-sea turbidites serve as valuable archives for reconstructing the history of large earthquakes. Offshore eastern Hokkaido is a key region for paleoseismic studies due to its high seismic activity and potential for generating large, destructive earthquakes. In this study, two piston cores were analyzed, primarily composed of dark grayish-yellow silt interbedded with thin layers of fine sand. These sediments were classified into three lithological units: turbidite sand (TS), turbidite mud (TM), and hemipelagic mud (HM). The turbidites are interpreted as earthquake-triggered deposits, as they exhibit well-graded sequences with sharp basal contacts that transition upward into finer silt and clay. The consistent stratigraphy and reproducible depositional patterns further support their interpretation as earthquake-triggered turbidites. Age-depth models are established using four methods: (1) Paleomagnetic Secular Variation (PSV), (2) radiocarbon dating of bulk sediment, (3) radiocarbon dating of selected specie of foraminifera, and (4) identification of volcanic ash. Synchronization of marine sediment records using PSV enabled an assessment of turbidite frequency and thickness over the past 5500 years. A total of 21 turbidite events were identified in cores PC01 and PC02 of a cruise KS19-12. Based on PSV ages, the results yield mean recurrence intervals of 225.3 ± 181.5 years (1σ) for PC01 and 258.5 ± 83.4 years (1σ) for PC02. These findings provide critical insights into the regional recurrence intervals, and the paleoseismic history of the lower Kuril Slope, particularly in the region eastern of Kushiro Canyon.