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

[MIS15-P04] Revised paleotsunami history at Kirikiri, Northeast Japan

*Takashi Ishizawa¹, Yusuke Yokoyama², Yosuke Miyairi² (1.International Research Institute of Disaster Science, Tohoku University, 2.Atmosphere and Ocean Research Institute, the University of Tokyo)

Keywords:Tsunami deposit, Radiocarbon dating

Tsunami deposits are defined as reworked sediment which is transported by a tsunami. The distribution area of tsunami deposits is often related to the inundation area of the tsunami and thus is useful for the reconstruction of paleotsunami. In general, age correlations of tsunami deposits were performed to identify tsunami deposits that were formed by the same tsunami. However, several problems (e.g., erosion and re-sedimentation by a tsunami, sample selection for ¹⁴C dating) make it difficult to accurately estimate the age of tsunami deposit. Herein, we conducted dating of tsunami deposits at Kirikiri, Iwate prefecture where paleotsunami history was not established well. ¹⁴C dating was performed by a few sample types at the same stratigraphic horizon. Our results indicated that wood samples showed younger age than the age of overlying sediments. Moreover, sediment from the same stratigraphic horizon with the wood also showed younger age than the age of overlying sediments. The reversion of age might be due to penetration of younger wood and surrounded sediment of the wood might also be affected by the wood. From the results, we revised the ages of paleotsunami deposits and our results were well consistent with the paleotsunami history of the surrounded area. Such detailed re-examination of paleotsunami ages was crucially important for the correlation of widely distributed tsunami deposits.