REEXAMINATION OF TSUNAMI SOURCE-EFFECT OF HETEROGENEOUS FAULT MOTION ON THE TSUNAMI GENERATION

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The standard mechanism of tsunami generation has been explained based upon the fault motion. A tsunami initial profile is given by the sea bottom displacement estimated from fault parameters, on assuming a homogeneous fault plane. This method often gives an unsatisfactory result different from the observed tsunami. The present study aims to examine causes of this difference.The 1983 Nihonkai-Chubu earthquake tsunami is selected as one of examples, for which many evidences and witnesses are available. The effect of the heterogeneous fault motion on the tsunami generation and propagation is discussed in view of the frequency dispersion and the resolution of tide record. In order to satisfy the witnessed tsunami, a secondary fault is necessary for the north fault and aseismic creeping slips on the eastern side of the south fault.As an example of the tsunami generated not by a fault motion, the 1883 Krakatau tsunami is well simulated, on assuming a rapid caldera formation and on developing a method to stabilize the computation at the early stage of computation.