[M-IS23_2AM1] tsunami deposit

[MIS23-07] Sediment transport induced by the 2011 Tohoku-oki tsunami: A shallow seafloor survey at southern part of the Sendai Bay

*Shuro YOSHIKAWA¹, Toshiya KANAMATSU¹, Izumi SAKAMOTO², Mikio FUJIMAKI³, Riichirou IMURA², Masatoshi YAGI², Kenji NEMOTO², Kazuhisa GOTO⁴, Hide SAKAGUCHI¹ (1.JAMSTEC, 2.Tokai University, 3.Coastal Ocean Research CO., LTD., 4.Tohoku University)

Keywords:shallow marine tsunami deposit, 2011 Tohoku-oki tsunami

After the 2011 Tohoku-Oki earthquake (Mw 9.0), to examine the tsunami-generated sediment transport and topographic change, and inundation area, a large number of investigations have been conducted on land, particularly at the coastal area of Sendai plain (e.g., Goto et al., 2012, 2014). Understanding the linkage of the transport between land and seafloor is also important. In the present study, to examine the influence of the tsunami and offshore sediment transport, high-resolution shallow seismic survey, sampling of surface sediments, vibracoring, and seafloor observation by underwater video camera were conducted on the shallow seafloor at the southern part of the Sendai Bay, northeastern Japan. The present study will help to understand not only modern sedimentary process induced by tsunami but also identification of paleo-tsunami records, because our knowledge of shallow marine tsunami deposits is limited in contrast to the subaerial tsunami deposits.One of the principal results is as follows. One or two sharp and continuous reflectors are recognized on the sub-bottom profiles in water depths approx. 6-15 m, excluding the area of outcrops in the southern part of the survey area. With decreasing water depth, depth of the reflectors from the seafloor generally increases (up to approx. 1.5 m). A comparison between the seismic profiles and vibracores infers that the sharp reflectors are erosional surface formed during the 2011 tsunami.