Abstract
Based on tide-gauge records observed at the Hokkaido and Sakhalin coasts facing the Okhotsk Sea, the characteristics of seven Kurile tsunamis (1918-1978) passing through the straits are investigated. The ratio of wave-heights at the Okhotsk Sea coast to Hanasaki located at the Pacific side was about one-half for tsunamis generating off the Urup Island, and the ratio has a tendency of decrease when the tsunami source moves to western direction toward Hokkaido. It suggests the effective tsunami energy passes into the Iturup Straits than other straits or channels. The travel time at Hanasaki becomes long when the tsunami source moves to the east direction, but that of the Hokkaido-Sakhalin region in the Okhotsk Sea is usually unchanged: For example, travel times of the Kurile tsunamis were mostly about 1.5 hours at Abashiri and 3 hours at Wakkanai. We found through the refraction diagrams that the unchanged travel times were caused by sea-bottom topography in the Okhotsk Sea. The wave rays emitted from the Iturup Straits concentrate in Sakhalin, while those from the Kunashiri Channel concentrate in Hokkaido. For future tsunamis coming-into the Okhotsk Sea, it is indispensable to take into considerations of the effect of tidal currents.
