遠地津波の数値計算に関する研究

その2太平洋を伝播する津波の挙動

抄録

The linear Boussinesq equation should be used in numerical simulations for distant tsunamis in the Pacific Ocean, because the dispersion effect is not negligible. Its difference equation which can not be expressed by an explicit scheme requires a long CPU time. One of the present authors has introduced a new technique, in which the first term of discretization error in the difference equation of the linear long wave theory was used and controlled to replace the physical dispersion term. This method is applied in the present study. The effect of ocean current on the tsunami propagation is confirmed to be negligible in wave direction and wave height. The 1960 Chilean tsunami is simulated. The Coriolis force has not only the effect on the propagation direction but also the dispersion effect, which is examined by comparing with the computed result without the Coriolis force. Effect of the sea bottom topography is examined in detail in terms of wave energy. About 40% of initial wave energy remains on the continental shelf in the neighborhood of Chile, and the rest is radiated to the Ocean. After scattered and trapped by islands and sea mounts, about 25% of the total energy arrives at Japan. The computed results shows a fairly good agreement with tide records after making correction of the effect of the water depth. For further discussions of the tsunami in shallow seas, simulations should be performed using the shallow-water theory and detailed topography.