Geological evidence of tsunamis in the past 3800 years at a coastal lowland in the Central Fukushima Prefecture, Japan

We found seven event deposits during the past 3800 years in a total of 16 geological core samples from a coastal lowland in Fukushima Prefecture, about 12 Inn north of the Fukushima Daiichi Nuclear Power Station. The event deposits consisted of well-sorted and rounded fine to coarse sand with single normal grading structures, parallel laminae, mud drapes, rip-up clasts, and erosional basal contacts. They were distributed about 2 km inland from the current shoreline and commonly became thinner landward. The third and fifth sand layers were characterized by many climbing ripples and parallel and trough-cross bedding that were probably caused by storm surges or some other events during the period of absent beach ridges. The other deposits were characterized by sedimentological features common to tsunami deposits. The top layer appeared to have been deposited by the 2011 Tohoku tsunami, and the second layer might have been resulted from the AD 869 Jogan Tohoku tsunami. The other three tsunami deposits corresponded to tsunami events between the second and fourth centuries AD, the sixth and fourth centuries BC, and the twelfth and ninth centuries BC. The average recurrence interval of the paleo-tsunamis was estimated to be 560-950 years. These dates are mostly consistent with previous studies of the Sendai plain, suggesting that paleo-tsunamis that reached the Sendai plain also reached the coast of Fukushima Prefecture. However, no trace was found from an earthquake around the 15th century, which had been considered as a predecessor of the 2011 Tohoku earthquake (Mw 9.0) in the tsunami deposit surveys in Sendai plain.