[H-CG28] Earth surface processes related to deposition, erosion and sediment transport

[HCG28-01] Sedimentary environment and earthquake history off Cape Muroto, SW Japan

*Juichiro Ashi¹, Toshiya Kanamatsu², Masafumi MURAYAMA³ (1.The University of Tokyo, 2.JAMSTEC, 3.Kochi University)

Keywords:contourite, turbidite, landslide

Submarine landslide morphology is developed off the east cost of the Cape Muroto. Baba et al. (2017, JpGU abstract) estimated that this landslide caused tsunami disaster at the Shishikui village during the 1512 Eisho earthquake by numerical investigation. Hakuho-maru KH-16-5 and KH-17-2 cruises conducted subbottom profile survey (SBP) using ROV "NSS" and surface sediment core sampling at the largest landslide of this region. However, these studies did not show any evidence for recent landslide sedimentation and deformation. On the other hand, Baba et al. (2019, Tectonophysics) discovered a recent landslide west of our survey site by high resolution swath bathymetric survey, and suggests possibility of tsunami generation by the submarine landslide. The old landslide studied by core sampling and SBP survey at a water depth of 1050 m shows characteristic morphology and sedimentary structures associated with coutour current. Sedimentary structure of core samples also indicates contourite deposition. Moreover, turbidite deposits are obtained at the base of this slope. Recurrence interval of deep-sea turbdites is similar to that at the adjacent confined basin (Iwai et al., 2004, Mem.Geol.Soc.Japan). Limitation of direct sediment supply through river to our study site suggests earthquake-triggered mobilization of the surface slope sediments.