In order to discover how the period of tsunami wave entering the straits between Seto Inland Sea and ocean affected to the wave amplitude inside the number of numerical experiments was carried out. The model wave with flat frontline was used for numerical modeling of tsunami propagation toward a coast and trough the straits between Japanese islands. Numerical tests were based on nonlinear shallow water system. For simulation we use regular modern personal computer with hardware acceleration, namely the FPGA (Field Programmable Gates Array) Calculator, which has been designed and tested earlier by the authors.