[M-IS11] Tsunami deposit

[MIS11-11] Paleotsunami history in the central Joban Coast during the last 6300 years

Yuito Sato¹, *Daisuke Sugawara², Takashi Ishizawa², Atsushi Urabe³, Yasuhiro Takashimizu⁴, Manabu Kato⁵, Tsuyoshi Kawata⁶, Kyohei Yoshioka⁷ (1.Graduate School of Science, Tohoku University, 2.International Research Institute of Disaster Science, Tohoku University, 3.Research Institute for Natural Hazards and Disaster Recovery, Niigata University, 4.Mathematical and Natural Sciences, Institute of Humanities, Social Sciences and Education, Niigata University, 5.Niigata Prefecture Archaeological Research Corporation, 6.Minamisoma City Board of Education, 7.Namie Town Board of Education)

Keywords:Paleoearthquake, Japan Trench

Since 2011, a lot of paleotsunami surveys have been conducted along the Pacific coast of the Tohoku region. Findings on paleotsunamis has become much more abundant than before. In particular, at several sites in the central to northern Sanriku Coast, paleotsunami records from the fall of the Towada-Chuseri tephra (To-Cu) to the modern era allows us to examine the timing and frequency of large tsunamis on a time span of 6000-7000 years. However, in the coasts of Sendai Bay and further south, paleotsunamis inferred from tsunami deposits so far dates back only to about 3000 years, and information on tsunami events older than about 2000 years ago is particularly limited.
In this study, we examined the paleotsunami history of the central Joban Coast, based on the analysis of cores collected from Ukedo at Namie Town, Fukushima Prefecture. Marsh deposits that have been continuously accumulated for the past 6300 years contained ten event sandy layers. Observations of sedimentary structures, diatom analysis and CNS analysis suggested that many of these sandy layers are tsunami deposits. The most recent event (Ev2) before the 2011 Tohoku-oki tsunami was correlated with the 869 Jogan tsunami, and the oldest event (Ev10) was dated at ca. 6200-5700 cal yr BP. Recurrence intervals of tsunamis estimated from the event ages varied from 200 to 800 years, suggesting irregular occurrence of giant tsunamis in the central Joban Coast.