[H-CG22] 堆積・侵食・地形発達プロセスから読み取る地球表層環境変動

[HCG22-01] タービダイトの挟在状況からみた日本海溝斜面域堆積物の地震動への応答の地理的変化

*池原 研¹、金松 敏也²、宇佐見 和子³ (1.産業技術総合研究所地質情報研究部門、2.海洋研究開発機構、3.日本エヌ・ユー・エス)

キーワード：海底堆積物、地震動、タービダイト

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.