The impacts of tides on extreme tsunami propagation due to potential Nankai Trough earthquakes in the Seto Inland Sea (SIS), Japan, are investigated through numerical experiments. Tsunami experiments are conducted based on five scenarios that consider tides at four different phases, such as flood, high, ebb, and low tides. The probes that were selected arbitrarily in the Bungo and Kii Channels show less significant effects of tides on tsunami heights and the arrival times of the first waves than those that experience large tidal ranges in inner basins and bays of the SIS. For instance, the maximum tsunami height and the arrival time at Toyomaesi differ by more than 0.5 m and nearly 1 h, respectively, depending on the tidal phase. The uncertainties defined in terms of calculated maximum tsunami heights due to tides illustrate that the calculated maximum tsunami heights in the inner SIS with standing tides have much larger uncertainties than those of two channels with propagating tides. Particularly in Harima Nada, the uncertainties due to the impacts of tides are greater than 50% of the tsunami heights without tidal interaction. The results recommend simulate tsunamis together with tides in shallow water environments to reduce the uncertainties involved with tsunami modeling and predictions for tsunami hazards preparedness.

Tsunami-tide interactions in the Seto Inland Sea (SIS) were investigated by taking into account the effects of tidal currents on the tsunami propagation in terms of the arrival time and the run-up heights along the coast of SIS. The initial tsunami wave profile was introduced by the possible Tokai-Tonankai-Nankai Earthquake of the magnitude Mw9.0, which is equivalent to that of 2011 Tohoku Earthquake. Numerical experiments with four different tidal phases, flood, ebb, high, and low, reveal that the water depth changes due to tides affect the tsunami propagation in terms of heights and arrival time. During high tides, the tsunami propagates faster and reaches higher than during the low tides. In addition, during the flood tides with rising water level, tsunami propagates faster than during the ebb tides. Further investigation also shows that the tsunami-tide interaction changes the tsunami signal such that the tsunami-only spectra shifts the spectral peaks after considering the tsunami-tide interactions. Local oscillation modes characterized by local bathymetry and topography shift to higher frequency modes due to the non-linear tsunami-tide interaction. To reduce the uncertainties involved in tsunami predictions and coastal defenses and management, it is strongly recommended to simulate tsunamis together with tides in shallow water environments.

No abstract