[M-IS23_2AM1] 津波堆積物

[MIS23-03] 仙台平野における歴史津波堆積物の化学組成と地球化学的判別方法の提案

*細田 憲弘¹、渡邊 隆広¹、土屋 範芳¹、山崎 愼一¹、中村 俊夫²、奈良 郁子¹、岡本 敦¹、平野 伸夫¹ (1.東北大学大学院環境科学研究科、2.名古屋大学年代測定総合研究センター)

キーワード：貞観津波堆積物, 東北地方太平洋沖地震, 地球化学

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.