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

根据断层运动解释了海啸发生的标准机制。海啸初始剖面由假定均质断层面的断层参数估计的海底位移给出。这种方法经常给出与观测到的海啸不同的令人不满意的结果。本研究以1983年日本海中部地震海啸为例，探讨了造成这种差异的原因。从潮汐记录的频散和分辨率两个方面讨论了断层非均匀运动对海啸发生和传播的影响。为了满足观测到的海啸，北断层需要一个次级断层，南断层东侧需要一个非断层蠕动滑动。作为一个非断层运动引起的海啸的例子，我们假设了一个快速破火山口的形成，并发展了一种在计算初期稳定计算的方法，很好地模拟了1883年喀拉喀托海啸。

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.