Tsunami Deposit and Environmental Change Associated with the 1498 Meio Earthquake Recorded at Yonezu Pond, Hamamatsu City, Japan

Abstract

 Array coring survey at the site of Yonezu Pond, which is depicted on a 1680s map, revealed a sand bed deposited by a tsunami caused by the 1498 CE Meio Earthquake occurred in the eastern Nankai Trough. This sand bed consists mainly of medium-grained sand, 10-15 cm thick, forming large ripples or dunes that record the reversal of tsunami inundation and return flows. Our age model based on radiocarbon dating limits the depositional timing of the sand bed to c. 1440-1600 CE. Only a tsunami could have generated a flow fast enough and long enough in duration to deposit a large amount of sand in Yonezu Pond, which at that time was more than 1.2 km inland from the coast and river. The facies change from peat to clay and pollen composition before and after the Meio tsunami suggest that the tsunami had a significant impact on the vegetation around the pond, especially herbaceous vegetation. Plant opal analysis revealed that paddy field devastation occurred with the formation of the Meio tsunami deposit.