[H-CG27] Turbidity current: from triggers for the generation to the depositional and morphologic al processes

[HCG27-05] Is surface sediment remobilization more popular mechanism for generating earthquake-induced turbidity current? Evidence of radiocarbon dates from the westernmost Nankai and Japan Trench subduction zones

*Ken Ikehara¹, Toshiya Kanamatsu³, Tobias Schwestermann², Arata Kioka², Michael Strasser² (1.Institute of Geology and Geoinformation, National Institute of Advanced Industrial Science and Technology, 2.Universität Innsbruck, 3.Japan Agency for Marine-Earth Science and Technology)

Keywords:surface sediment remobilization, turbidite, earthquake, radiocarbon dating

Deep-sea turbidite has been used for reconstructing past large earthquake history. Surface sediment remobilization is a relatively new idea for generating earthquake-induced turbidite, although submarine landslide has been considered as major mechanism for earthquake-induced turbidite deposition. Surface sediment remobilization has been reported from the Chilean lakes, forearc slopes along the Nankai and Japan Trench subduction zones. However, the detailed mechanism of surface sediment resuspension, remobilization and initiation of turbidity current is still unknown. For better understanding of the mechanism, it is important to understand the spatio-temporal occurrence of surface sediment remobilization. We obtained some cores from a small basin on the forearc slope in Hyuga-nada off Kyushu, and the Japan Trench floor. Fine-grained turbidites were found in the cores. Paired radiocarbon dates of the turbidite muds and hemipelagic muds between the turbidites show only small age differences. This indicates that it is unnecessary to occur bathymetry-scale (with >several meters bathymetric change) submarine landslides by earthquake ground shaking for generation of the turbidites. Large surface sediment resuspension by earthquake ground shaking at the sedimented slope near the depositional area (basin) is thought to be an important process for repeated deposition of earthquake-induced turbidites in the basin.