Wave Source of the Hawaii Tsunami in 1975 and the Tsunami Behavior in Japan

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  • 1975年ハワイ島 (Kalapana) 津波と日本沿岸での挙動
  • 1975ネン ハワイトウ Kalapana ツナミ ト ニホン エンガン デ

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The Kalapana tsunami was generated off the south coast of Hawaii Island, accompanying the earthquake of magnitude Ms=7.2 (NOAA), at 14h 48m (GMT), Nov. 29, 1975. Some features of this tsunami are investigated on the basis of tide gauge records of NOAA and Japan, adding the reports of the US field investigation.<br>Tsunami magnitude of the Imamura-Iida scale is decided as m=2, judging from the tsunami heights observed near and distant fields. The initial motion of the tsunami waves was in an upward direction at the whole Hawaiian stations, suggesting the uplift of the sea-bottom in the tsunami source area. The source dimension of tsunami is inferred to be 70km along the south coast of Hawaii Island, and the area is 2.2×103km2. By applying the corrections for the refraction and shoaling from the inundation heights at the Hawaii Island, the average vertical displacement of 1.2m would be occurred in the source area. The tsunami energy of approximately is 1.6×1020 ergs. According to statistical relation, the present tsunami is large compared with the earthquake magnitude.<br>The tsunami fronts arrived in NE Japan at about 7h 40m after the occurrence of the earthquake. The maximum double amplitude is 20-30cm with the period of about 15min and the amplitude is relatively higher than that in SW Japan. It is noticed that the wave rays emitting the tsunami source concentrate in the Kuril Islands.

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