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

本研究的目的是将湖泊沉积物中的海啸痕迹与历史地震记录联系起来。为了达到这一目的，我们开发了覆盖层，在覆盖层中收集地表沉积物是可能的。为此研制了小型振动锤的活塞盖、重力盖和取芯附件。在高知县Susaki市Tadasuga-ike使用这些岩心采样器采集了7个岩心样本。Tadasuga-ike是肉水池塘，在首和南开地震中被海啸海水入侵。在底面以下35-40cm、40-45cm和60cm处观察到明显的彩色层。60cm层存在海相钙质纳米化石，说明当时有海水流入。采用Pb210法测定岩心样品的沉积速率。SS02-04和ss07岩心沉积速率分别为1.0 cm/yr和0.9 cm/yr。这些速率表明60厘米厚的地层是在60年前形成的，与首洼南开地震相对应。

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.