ASsudy on the improvement of far-field tsunami waming system

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For the improvement of the accuracy of far-field tsunami warning system, we studied (1) Mechanism and characteristics of multiple reflection of tsunamis incident on a continental shelf, (2) An estimation method of tsunami source region by using the real-time observation data, (3) Characteristics of dispersion effect of tsunami during the propagation and run-up process.For the study (1), we derived an analytical solution of tsunamis which are obliquely incident on a offward-finite constant slope. The incident waveforms are assumed to be transient. Based on the solutions obtained, characteristics of transient tsunami propagations on the slope are discussed in terms of the several conditions of incidence such as horizontal incident wave scale, incident angle and incident waveform. When tsunamis are incident almost parallel to the shoreline, multiple reflected waves reveal and are trapped on the slope. The solution indicates that the interference between multiple reflected waves and incoming incident waves could be a contributing cause of conspicuous amplification of tsunamis on the slope.For the study (2), we developed an estimation method for tsunami source region by using the hypothetical offshore tsunami gauge. The method enables to estimate the fault parameters of W and L (Width and Length), which reflects the horizontal extent of tsunami source region, within 20 % of estimation errors.For the study (3), we developed a numerical model with Boussinesq-type equations, which enables to estimate the dispersion effect during the process of tsunami propagation and run-up. The model was validated through the case study of the 1983 Nihonkai-Chubu earthquake tsunami to obtain the better estimate of tsunami height to explain the observed tsunami height along the coast of Japan sea.