Tsunami records of Showa, Ansei and Houei Nankai earthquakes in lake sediments.

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The purpose of this study is to relate the tsunami traces in the lake sediment and the historical earthquake records. In order to achieve this purpose, we developed corers in which to surely collect the surface sediment is possible. Small piston corer, gravity corer and coring attachment for small vibration hammer were newly made for this study.Seven core samples were collected by using these core samplers in the Tadasuga-ike, Susaki City, Kochi prefecture. Tadasuga-ike is flesh water pond and was invaded by sea water of tsunami at the Shouwa Nankai earthquake. Remarkable colored layers ware observed at the 35-40cm, 40-45cm and 60cm beneath the bottom surface. The presence of marine calcareous nannofossils at the 60cm layer indicates that sea water flowed in the pond at that time.Pb210 method was used for determination of sedimentary rate of core samples. The sedimentary rate of core SS02-04 and 07 was 1.0 cm/yr and 0.9 cm/yr respectively. These rates mean that the remarkable 60cm layer accumulated about 60 years ago and correspond to the Shouwa Nankai earthquake.