[S-CG52] Ocean Floor Geoscience

[SCG52-21] Paleoseismology based on deep sea thick-turbidite in Japan Trench: their stratigraphy and depositional mechanism using paleo and rockmagnetic studies

*Toshiya Kanamatsu¹, Ken Ikehara², KanHsi Hsiung¹ (1.Japan Agency for Marine-Earth Science and Technology, 2.National Institute of Advanced Industrial Science and Technology)

Keywords:Japan Trench, Huge erthquake, turbidite, paleomagnetic secular variation

Distinctive thick turbidite beds in deep sea basin of Japan Trench induced by huge earthquakes were reported by recent studies. We additionally studied two sediment cores at 39°N to investigate their distribution of the thick turbidite further north along the Japan Trench and understand their depositional mechanism in the narrow elongated deep-sea basin. We studied the detailed stratigraphy of turbidite beds using paleomagnetic secular variation. The method of anisotropy of magnetic susceptibility was applied to investigate the depositional conditions of each turbidite bed. The obtained ages of turbidite beds in this study closely approximate the historical and pre-historical huge earthquakes off Tohoku, northeastern Japan. The hydrodynamic condition during deposition of turbidite are inferred from their grain alignment based on AMS data. The directions of basal and upper thick muddy part of a turbidite bed are not always consistent, which suggests the hydraulic condition in the narrow elongated deep-sea basin. This fact could be essential information to elucidate a unique hydraulic condition during the turbidite deposition in the confined basin in the Japan Trench.