[M-IS11] tsunami deposit

[MIS11-P05] Sediment environment change from diatom analysis in Hirota Bay

*Kosuke Tsutsumi^1,2, Izumi Sakamoto¹, Yuka Yokoyama¹, Rihoko Saito^1,3, Naoki Haramishi^1,4 (1.Tokai University, 2.IEDA Consultants, Inc., 3.Arc Geo Support Co., Ltd, 4.FUKADA SALVAGE & MARINE WORKS CO., LTD)

Keywords:Diatom, Tsunami

The Tohoku great earthquake disaster that occurred on March 11, 2011 gave tsunami damage to the wide range of the Tohoku district. In this study,we aimed for clarifying the sedimentation environment change after the tsunami in the Hirota bay. We performed sound wave exploration, particle size analysis, diatom analysis in this study. As the result, next 1-3 characteristics become clear. 1)Sabulosity sediment is superior in the coastal place, and a particle becomes small off the coast.2)Around Kesen-gawa river, the existence of the coarse sand to gravel zone that formed NW-SE trending was confirmed. 3)Nature of the muddy fine grain sediment is superior in the Karakuwa peninsula side of the gulf west and is sabulosity sediment superiority in the Hirota Peninsula side of the gulf east side. As a result of diatom analysis, freshwater species was dominant in the shore area, and confirmed that the ratio of freshwater species decreased as an offing.