[S-CG48] Ocean Floor Geoscience

[SCG48-P20] Large Holocene submarine landslide deposits at the Kuril trench: insights into the size and transportation processes

*Yu-Chun Chang¹, KanHsi Hsiung¹, Toshiya Kanamatsu¹, Yuhji Yamamoto² (1.JAMSTEC, 2.Kochi Univ.)

Keywords:submarine slope failure, turbidite/debrite, paleomagnetic, hazard assessment

Recurrent giant subduction zone earthquakes can trigger large submarine landslides on the continental slopes, causing seafloor foundation damage and tsunami threats. Understanding the volume, origin and types of submarine landslides is crucial to assessing landslide impacts and associated hazards. This study identified a potential large submarine slope failure by analysing six-piston cores along the Kuril trench (approximately from offshore Nemuro Peninsula at east to offshore Hiroo at west). Stratigraphy and turbidite textures were reconstructed using various techniques, including visual core observations (VCD), X-ray computed tomography (X-CT), X-ray fluorescence (XRF), magnetic properties, and bulk ¹⁴C analyses. A thick Holocene debrite, approximately 5 m thick, was discovered at the easternmost core, characterised by large, chaotic, and poorly sorted clasts within the fine-grained matrix, a sharp basal contact and a high concentration of magnetic minerals. Geochemical similarities extend this debrite over at least >70 km to the cores at the downslope of the Kushiro Submarine Canyon, although the exact distance should be greater due to the absence of cores further to the right. Moreover, sedimentary structures for the same event bed on the left cores were transformed into laminated, graded, and fining upward beds, suggesting a flow evolution from a cohesive debris flow to a low-concentration turbulent flow. The directions of paleocurrent, as reoriented by anisotropy of magnetic susceptibility (AMS) and natural remanent magnetisation (NRM), are not entirely aligned with the main sediment flow direction, which may indicate a complex interaction between flow and the seafloor topography. Future efforts will address the completed extent of this large submarine landslide, the initial failure depth of the submarine landslides, and the implications of the direction deviation between magnetic material and sediment flow.