[H-CG22] Earth surface processes related to deposition, erosion and sediment transport

[HCG22-01] Spatial difference in response of slope sediments to earthquake ground shaking along the Japan Trench from turbidite records in slope and trench basins

*Ken Ikehara¹, Toshiya Kanamatsu², Kazuko Usami³ (1.Institute of Geology and Geoinformation, National Institute of Advanced Industrial Science and Technology, 2.Japan Agency of Marine-Earth Science and Technology, 3.Japan NUS)

Keywords:marine surface sediment, earthquake ground shaking, turbidite

Earthquake-induced turbidites have been formed by several processes including submarine landslides and surface sediment remobilization. Response of slope and slope sediments to earthquake ground shaking spatially changes with characteristics of slope and slope sediments such as slope gradient, sediment grain-size and composition, sedimentation rate, geotechnical and mechanical properties and mode of earthquakes around the slope. However, such change has been poorly understood. Comparison of turbidite recurrence patterns in the different nearby basins may be basic information for this discussion. We examined sediment cores collected from basins at the mid-slope terrace (MST) and trench floor along the Japan Trench. In the central Japan Trench at ~39 N, stratigraphic records of some historical and paleo- earthquakes in the MST and trench basins are the same, suggesting similar response of the upper and lower part of the lower landward (inner) slope, while in the northern Japan Trench at ~40 N, turbidite occurrence in the MST basin core is much higher than that in the trench basin core, suggesting difference in response between the upper and lower part. Along the MST, turbidite occurrence in the core (12 turbidites during the last ~4 ky) at ~39 N is smaller than that (26 turbidites during the last ~23 ky) at ~40 N even smaller threshold of the peak ground acceleration (PGA) by earthquake for turbidite deposition at ~39 N (~0.4 g) than at ~40 N (~0.6 g). Frequent occurrence of large (M7-class) earthquakes in the northern Sanriku may contribute to high frequency in turbidite deposition at ~40 N and seismic strengthening of surface sediments by large earthquakes is a possible mechanism for high value of the PGA threshold.