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|タイトル: ||32. 1983年日本海中部地震津波の規模および波源域|
|その他のタイトル: ||32. Tsunami Magnitude and Source Area of the Nihonkai-Chubu(the Japan Sea) Earthquake in 1983|
|著者: ||羽鳥, 徳太郎|
|著者(別言語): ||Hatori, Tokutaro|
|掲載誌情報: ||東京大学地震研究所彙報. 第58冊第3号, 1984.1.14, pp. 723-734|
A tsunami was generated off the coast of Akita and Aomori Prefectures, the Japan Sea, at 1200hours(JST) on May 26, 1983. According to JMA, the epicenter of the main shock was located at 40°22′N, 138°54′E, with a depth of 10km and an earthquake magnitude of M=7.7. Based on tide-gauge records, the source area, magnitude and propagation of the present tsunami are investigated. The source area estimated by means of an inverse refraction diagram is 1×10^4km2, extending 140km parallel to the bathymetric line of 2,000m. The eastern margin of the tsunami source was located 10-20km from the coast. The source area of the tsunami covers the aftershock area. The initial motion of the tsunami began with a conspicuous down-ward direction at the tidal stations from Esashi to Funakawa on the eastern side of the source area, while the other stations was in an upward direction. This suggests that the sea bottom on the east side of the tsunami source subsided and that on the west side uplifted. Judging from the attenuation of tsunami height with distance, the magnitude(Imamura-Iida scale) of the present tsunami is m=2.5. This is relatively high for an earthquake having a magnitude of M=7.7. A short-period wave of about 10min was predominant. In the refraction diagram, it can be seen that the distribution of tsunami energy was controlled by the submarine topography. The tsunami energy concentrated at Okushiri Is., the north of Sado Is. and the tip of Noto Peninsula. The east coast of Korea(37°～38°N) also suffered severe damage two hours after the earthquake occurred. The duration time of the tsunami was longer than that of tsunamis generated at the Pacific side because of strong reflected waves from the continental coasts. In a map of the source distribution of the past tsunamis since 1700, the source areas line up in three zones on the coast, the continental shelf and the bathymetric line of 2,000-3,000m. Large tsunamis have been generated in the deep sea. After the present tsunami generation, there are still many gaps of tsunami source areas in the Japan Sea region.