著者

羽鳥 徳太郎

出版者

東京大学地震研究所

雑誌

東京大學地震研究所彙報 = Bulletin of the Earthquake Research Institute, University of Tokyo (ISSN:00408972)

巻号頁・発行日

vol.54, no.3, pp.543-557, 1980-03-31

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Adding tsunami data reported by the U.S.S.R. sources, tsunami magnitude and the source area of the tsunamis generated in the Hokkaido and Kurile regions during the period from 1893 to 1978 are re-examined. The source dimension and magnitude of the tsunamis generated in the Hokkaido region correspords well with the earthquake magnitude. However, the tsunamis in the Kurile region have varied behaviors. The two Kurile tsunamis of Oct. 20, 1963 and June 10, 1975 were especially abnormal in comparison with other tsunamis accompanied by similar earthquake magnitude. In most cases, the initial motion of the tsunamis was observed with upward direction, but the Kurile tsunamis of Aug. 11, 1969 and June 10, 1975 began with a conspicuous downward motion at the Hokkaido and Kurile tide stations. The source areas of the tsunamis that accompanied large earthquakes (M>8) line up along the continental slope near the Kurile trench and the 1973 Nemuro-oki tsunami was generated in the seismic gap between the 1952 Tokachi-oki and the 1969 Shikotan earthquakes. However, the source area of the 1973 tsunami occupies only the eastern half of the 1894 tsunami source. After the 1973 Nemuro-oki tsunami, the tsunami activity moves to the northeastern direction along the Kurile trench. These source areas fall in the southern part of the source areas of the 1958 Iturup and the 1969 Shikotan tsunamis. In the space-time diagram of the earthquakes having a magnitude of M≧7, remarkable gaps can be seen in the west side of the 1973 tsunami source and off Urup Island. It is possible that a future tsunami of magnitude m~2 may be generated, accompanying the release of seismic energy in the two regions.