[M-IS23_2AM1] tsunami deposit

[MIS23-03] Chemical composition of historical tsunami deposits in the Sendai plain and proposal of geochemical discrimination

*Norihiro HOSODA¹, Takahiro WATANABE¹, Noriyoshi TSUCHIYA¹, Shin-ichi YAMASAKI¹, Toshio NAKAMURA², Fumiko NARA¹, Atsushi OKAMOTO¹, Nobuo HIRANO¹ (1.Graduate School of Environmental Science, Tohoku University, 2.Center for Chronological Research, Nagoya University)

Keywords:Jogan tsunami sediments, The 2011 Tohoku tsunami, geochemistry

A magnitude 9.0 earthquake and huge tsunami occurred off the Pacific coast of Tohoku area in Northeast Japan. After the 2011 Tohoku earthquake and tsunami, disaster science is much focused to reduce the damage around costal area, and it plays an important role as making the set of guidelines in an emergency. Because Japanese islands are located on the plate boundaries among the Pacific, Eurasian, Philippine Sea and North American plates, large earthquakes and tsunamis have repeatedly occurred during historic and prehistoric times. A huge tsunami more than 10m-height is often accompanied with submarine earthquakes around the Pacific Rim. The 2011 Tohoku tsunami was the one of the most destructive natural disasters. By the effect of that, study on earthquakes and tsunami become more and more significant, and it a major issue of social concern in Tohoku and other areas. After the 2011 Tohoku tsunami, these invasion areas were covered by a huge amount of tsunami deposits more than 10 million tons. In addition, we are able to obtain past tsunami deposits with the age of ~1000-2000 years before present (BP) in the same area using boring corer. In order to make an expecting tsunami invasion map in other areas as soon as possible, we must provide the information about the distribution of past tsunami deposits. However, it is difficult to discriminate the one of tsunami and other events, such as storm and flood. Additionally, we must establish a new technique to detect invisible muddy and thin tsunami deposits. We need historical archives and geological proxy of past tsunami invasion, but it is rare to have both evidences in many cases. Geochemistry is useful techniques to know the source of terrestrial deposits and these weathering processes. Therefore, we tried to apply geochemical techniques in this study.