TSUNAMI GENERATION WITHOUT SHAKING DUE TO EARTHQUAKES.

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A tsunami is ususlly considered to be generated by an earthquake. Once fault parameters are given, the initial tsunami profile is calculated with the elastic theory. It is assumed that the vertical displacement of sea bottom is closely related to the fault movement. However, this assumption is not always true.1) In case of the 1983 Nihonkai-Chubu earthquake composed of two faults, a secondary fault in the north fault and a non-seismic movement are necessary in order to explain earlier arrival of the actual tsunami than the computed tsunami for the major fault movement determined by seismic data.2) In case of the 1992 Nicaraguan tsunami, in spite of a large tsunami, the earthquake was very weak, as 2 in the JMA intensity scale. Whether this tsunami was generated by the earthquake or by other mechanism was examined. It is concluded that this earthquake was a tsunami earthquake.3) In case of the 1993 Hokkaido Nansei-oki earthquake, the first tsunami arrived at the western coast of Hokkaido 5 minutes faster than that generated at the place of the fault estimated from seismic data. This strongly suggests that other tsunami generation mechanism than the earthquake should be found in the area between the fault and the coast.4)The 1883 Krakatau tsunami which was not generated by an earthquake but by a caldera formation was numerically simulated. A method is developed to stably simulate a sudden fall of water at the initial profile.