著者

Hatori Tokutaro

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.47, no.6, pp.1063-1072, 1969-12-20

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The wave source of the tsunami generated off West Hokkaido (Shakotan Peninsula), in the Japan Sea, on Aug. 2, 1940 is estimated by means of an inverse refraction diagram, making use of a new bathymetric chart. The source area extends 170km in the NNW-SSE direction, which is smaller than that obtained by Miyabe (1941). However, the dimension estimated by the present analysis is still large for the earthquake magnitude of M=7.0. From a comparison of the geographic distribution of the earthquake intensity with those of the other tsunamigenic earthquakes that occurred in the Japan Sea, the magnitude of this earthquake is investigated. Effective tsunami height observed on the surrounding coasts of the Japan Sea can be explained by the direction of the present source. Magnitude of the tsunami of 1940 seems to be equal to that of the Niigata tsunami of 1964 and is represented as m=2. Besides, the wave source of the tsunami generated off Rumoi, West Hokkaido, on Nov. 4, 1947 is discussed, taking the aftershock area into consideration.|1940年8月2日,北海道積丹沖に起きた津波は日本海全域に伝播し,北海道西岸をはじめソ連の沿海州と北朝詳,隠岐にも家屋,船舶などに被害を与えた,地震の規模Mは,気象庁の地震カタログ(1958)によるとM=7.0, USCGSによるとMG=7.7と示されており,両者の決定値には著しい違いがある.一方,余震は札幌において多数観測され,P-S頻度分布は10 secから33 secの範囲にあつて,余震域の長さは約190kmと推定されている(宇津,1961)