[S-CG55] 海洋底地球科学

[SCG55-26] Extensive Thick Turbidites in the Southern Kuril Trench: Evidence of the 13th Century Giant Earthquake?

*Yu-Chun Chang¹、KanHsi Hsiung¹、Toshiya Kanamatsu¹、Yuhji Yamamoto²、RYO NAKANISHI³ (1.Japan Agency for Marine-Earth Science and Technology、2.Marine Core Research Institute, Kochi University、3.Graduate School of Science, Kyoto University)

キーワード：Megaearthquake, Turbidite, Kuril trench, Core analysis, Submarine landslide, Paleomagnetic secular variations

Earthquakes can generate intense ground shaking and high tsunami waves, leading to loss of life and property. Assessing the timing and impact areas of large paleo-earthquakes, particularly those of giant earthquakes (Mw ~9), is crucial for improving hazard prediction. Thick turbidites in subduction zones are found to be valuable records of large paleo-earthquakes, as strong seismic shaking can mobilize substantial unconsolidated sediments from submarine slopes. In this study, five piston cores were collected along the axis of the southern Kuril Trench (approximately from offshore Nemuro Peninsula at the east to offshore Hiroo at the west) during the cruise in 2017 and 2024. Among them, thick turbidites (1–5 m) were identified in all cores and were interpreted as products of the same seismic event based on the similarity in sedimentological structures, geochemical intensity, magnetic characteristics, and occurrence time. Core correlations suggest that the turbidite distribution extends at least 100 km within the trench basin, though the full extent is likely greater considering the incomplete core coverage. The total turbidite volume, estimated from turbidite thickness and basin areas, is approximately 1-2 km³. The magnetic fabric orientation derived from the coarse-grained divisions of turbidites indicates that sediment flow entered the trench near the toe of Kushiro Canyon and subsequently moved northeast and southwest of the trench. A high-resolution age-depth model, developed using paleomagnetic secular variation data, indicates that these turbidites were emplaced between 680 and 760 BP, likely corresponding to the 13th-century giant earthquake. This study represents the first direct linkage of thick submarine turbidites to a historical giant earthquake in the southern Kuril Trench region. Future work will focus on simulating the turbidite emplacement process to identify the initial slope failure areas.