日本沿岸で観測したコロンビア・ペルー津波(1960年～1979年)

概要

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During the past 20 years (1960-1979), five tsunamis generated off Colombia and Peru were observed by tide-gauges in Japan. Based on these tide-gauge records, the magnitude and behavior of the Colombia-Peru tsunamis were investigated. According to the PDE (U.S.A.) reports, the earthquake magnitudes of the surface waves were in the range of Ms=7.5 to 7.9. The magnitude of the Colombia earthquake on Dec. 12, 1979 was the largest. The aftershock areas of these earthquakes except for the earthguake on May 31, 1970 lay on the continental slope, parallel to the bathymetric contours. The lengths of the aftershock areas were 120-200 km. According to the author's method based on the attenuation of tsunami height with distance, the tsunami magnitudes (Imamura-Iida scale: m) of the Colombia-Peru tsunamis were determined to be m = 2 to 2.5. Along the coast of Japan the maximum double amplitudes of these tsunamis averaged about 20 cm. The amplitudes in northeastern Japan were recorded with a localized maximum of about 40 cm. The period of the tsunamis observed at most of the tide stations was 15 min, not as long as that of the 1960 Chile tsunami. The initial wave front of the Colombia tsunami reached northeastern Japan in 19.5 hours, and then propagated along West Japan 1.5 hours later. The Peru tsunamis took 20 to 21.5 hours. The more southernly the South American tsunami source the longer the tsunami takes to reach Japan.
1982-01-08