Possible paleo-tsunami deposits at Rikuzentakata City, Japan

Rikuzentakata City, NE Japan, has been repeatedly suffered by tsunami inundations including 1896 Meiji-Sanriku, 1933 Showa-Sanriku, 1960 Chilean Tsunami, and 2011 Tohoku-Oki Tsunami. Up to 30 cm thick sand layer was deposited by the 2011 tsunami in this city (Naruse et al., 2012). Our study indicates that historical and prehistoric tsunamis also left deposits in this area. Nevertheless, previous studies of paleo-tsunami deposits in this area are limited (Haraguchi et al., 2006, Imaizumi et al., 2007), because of the difficulty of finding paleo-tsunami deposits along this ""ria"" coast. We conducted a field survey using a geoslicer to acquire sediment cores in order to explore the magnitude and history of tsunamis in this area. Overall 10 cores, each 2 m long and 12 cm wide were acquired during the survey. The sedimentary sequences were mostly composed of peaty soil, which was thought to have been deposited in a marsh environment, however these soils units were inter-fingered by numerous 1-15 cm thick sand layers. According to initial work including grain size analysis, some of the sand layers deposited 1.4 km from the present shoreline are identified as having a possible tsunami origin because they tend to show upward fining characteristics, indicating rapid sedimentation from suspended load. We will also present the preliminary results of tephra chronology, radiocarbon and 210Pb dating, and diatom analysis.Possible paleo-tsunami deposits at Rikuzentakata City, Japa