2015 年 2015 巻 43 号 p. 53-60
Research of tsunami deposits greatly increased after the 2011 off the Pacific coast of Tohoku earthquake and tsunami. However, historical or paleo-tsunami deposits are buried under the topsoil, and thus we generally conducted coring survey and correlate tsunami deposits between each other site based on lithology, age and so on. Correlation of each layer of tsunami deposits is very significant for assessment of tsunami frequency and risk. In this study, we carried out very close interval (2.5 m interval) array Handy Geoslicer survey to confirm continuity of tsunami deposits. Additionally, we changed the interval of coring sites and tried to compare the correlation of each tsunami deposits. Consequently, we correlated each tsunami deposits confidently in 2.5 m, 5m, and 10 m interval. In 20 m and 50 m interval, we can correlate some tsunami deposits, however accuracy of the correlation is much lower than those of 2.5 m and 5 m interval. Although such feature varies regionally, it is important to discuss about relation between coring interval and accuracy of information obtained from them. On the other hand, we observed that one tsunami deposits did not necessarily show same characteristics (thickness, composition, and sedimentary structure) along the survey line, and re-realize the difficulty and complexity of correlation of tsunami deposits. This study is one case study, thus we need to conduct similar discussion at other sites and examine the accuracy of correlation in the future.