[M-IS15] Tsunami deposit: research progress after the 2011 Tohoku-oki earthquake and prospects

[MIS15-P01] A study for correlation of mega-tsunami in the Kuril Trench based on the tsunami deposits in the Erimo area, Hokkaido

*RYO NAKANISHI¹, Juichiro Ashi^1,2, Yosuke Miyairi¹, Yusuke Yokoyama^1,3 (1.Atmosphere and Ocean Research Institute, The University of Tokyo, 2.Graduate School of Frontier Science, The University of Tokyo, 3.Department of Earth and Planetary Sciences, Graduate School of Science, The University of Tokyo)

Keywords:Tsunami deposits, Kuril Trench, Radiocarbon dating, Hokkaido, Numerical simulation

In order to clarify the spatial diversity of the rupture mode of giant earthquakes with recurrence intervals of hundreds to thousands of years, it is necessary to obtain information from a geological record such a tsunami deposit, because observational data alone are insufficient. In the southern part of the Kuril Trench, the geological studies reveal the existence of giant earthquakes that cannot be explained by the earthquakes observed (Sawai, 2020). These giant earthquakes have intervals of several hundred years, and the last one is said to have occurred in the 17th century. However, there have been few cases of comparing the ages of sand layers at different sites, and the spatio-temporal distribution of fracture areas over long-time scales has not been clarified. In this study, we focused on the east coast of Erimo, which has not been investigated, and examined the magnitude of the 17th century tsunami and the possibility of contrasting older events. In the Erimo town, 8-10 sand layers were found during the past 4000 years, which were judged to be tsunami deposits based on their supply from the beach sand and anomalous distribution. Numerical simulations showed that the 17th-century tsunami can be explained by the same rupture zone as the 17th-century tsunami widely observed in eastern Hokkaido (Ioki and Tanioka, 2016). The ¹⁴C dating results show that the depositional ages of the sand layers in this area are similar to those of the sites facing the Tokachi-oki segment, while some sand layers do not have candidates comparable to those of the sites facing the Nemuro-oki segment. The age of the sand layers in the area west of Erimo Cape also correlated with the age of the sand layers in the southern part of Hidaka, suggesting that the sand layers in the southern part of Hidaka are likely to have originated from the giant earthquake in the Kuril Trench.