| Summary: | application/pdf Based on tide-gauge records of Japan and other far-field data, the magnitudes of the Kurile-Kamchatka tsunamis during the past 77 years (1904-1980) are investigated. The features of a few tsunamis differ greatly. For example, the Kamchatka tsunami of Apr. 13, 1923 and the Kurile tsunami of Oct. 20,1963 which accompanied earthquakes with magnitudes of M=7.2-7.3 inundated the coastal areas near the tsunami source 10-20 meters. According to the author's method based on the attenuation of wave-height with distance, the magnitudes (Imamura-Iida scale, m) of these tsunamis are estimated to be m=2.5 and 2 respectively. The magnitudes of several tsunamis judged from the near-field and far-field data were a little different. At the Hokkaido and Sanriku coasts, North Japan, the waveheights (above ordinary tides) for the Kurile tsunamis with m=2.5-3 were 1.0-1.5 meters and 0.5 meters respectively. However, the distribution of the wave-heights for the Kamchatka tsunami was different. The wave-heights on the Sanriku coast were greater than those on Hokkaido. The great 1952 Kamchatka tsunami (m=4) inundated the Sanriku coast 2-3 meters. The wave-heights increased especially in the bays with the seiche of 43 min and 20 min. In the map of the source distribution, a tsunami (seismic) gap of 400-500 km exists along the trench in the North Kurile and West Aleutian Islands regions. In order to predict the travel times of tsunami along the Kurile and Japanese coasts, the refraction diagrams of two imaginary sources are drawn. ...
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