Geological Survey Research of Past Tsunamis by Detecting Traces of Deposit in Sediment Layers in Lagoon Beds and Sea Shores

对过去海啸的地质痕迹进行了探测研究。Okamura和Tsuji在纪伊半岛的两个湖泊的泻湖床的底部沉积物层中发现了薄砂层，这是历史和史前海啸形成的。这两个湖泊是小濑市的大池泻湖和纪伊长岛町的Suwa-ike泻湖。他们在大池泻湖的取芯样品中发现了十多个砂层，并通过C-14方法测定了它们的年代，阐明了它们是由一系列大东海地震形成的，最古老的一个显示了公元前6世纪的事件。志贵和山崎在赤塔半岛尖端附近的岩石海岸中新世地层中发现了海啸的痕迹，西村发现了1640年由北海道驹岳火山爆发引发的海啸形成的砂层。此外，还在北海道东部沿岸的沼泽地进行了沉积物层的探测。此外，我们还在巴布亚新几内亚北部海岸a进行了海啸痕迹探测的地质研究。西村对拉包尔附近的火山喷发所产生的海啸的地质痕迹进行了实地调查，而津治则对1998年的艾塔佩地震的海啸进行了研究。

Studies of detection of geological traces of past tsunamis were made. Okamura and Tsuji found out thin sand layers, which were formed historical and pre-historical tsunamis, in the bottom sediment layers on the lagoon bed of two lakes on the cast of the Kii Peninsula : O-ike lagoon in Owase city, and Suwa-ike lagoon in Kii-Nagashima Town. They detected more than ten sand layers in the coring samples obtained at O-ike lagoon and dated them by C-14 method, and clarified that they were formed by a series of major Tokai earthquakes and the oldest one shows the event of 6 century BC.Shiki and Yamazaki detected traces of tsunamis in the layer of the Miocene epoch in the rock shore near the tip of Chita peninsula, Aichi prefecture.Nishimura found out a sand layer formed by the tsunami of 1640 generated by the eruption of Komagatake volcano, Hokkaido, on a coast of the Funka Bay. He also detected sediment layers in swamps besides the coast of the eastern Hokkaido.In addition, we made geological research of tsunami trace detection on the north coasta of Papua New Guinea. Nishimura made field survey of geological traces of the tsunamis generated by an eruption of a volcano near Rabaul, and Tsuji made a study on the tsunami of the 1998 Aitape Earthquake.