EFFECTS OF TIDE AND WAVE DIRECTIONALITY ON LOCALIZED TSUNAMI-INDUCED CURRENTS IN PORT AND HARBORS

Abstract

Here, we present the results of a numerical modeling study to investigate how the maxima of the tsunami-induced currents vary due to dynamic effects of tides and wave directivity. A sensitivity analyses was conducted in three harbors by coupling the tsunami with the tide signal at twelve different tide levels. We find that tsunami-tide interaction can change the maximum current speed experienced in a harbor by up to 25% for the events and harbors studied, and that this effect is highly site-specific. To evaluate the effect of wave directionality on maximum currents, three earthquakes with different magnitudes were devised along the Pacific, which were also tuned to create the same maximum near-harbor amplitude. Our analysis also shows that, for the harbor and sources examined, the effect of offshore directionality and tsunami frequency content has a very weak effect on the maximum currents experienced in the harbor. The much more important dependency on maximum currents is on the near-harbor amplitude of the wave, indicating that currents in a harbor from a tsunami generated by a large far-field earthquake may be reasonably well predicted with only information about the predicted local tsunami amplitude. This study was motivated by the hope of constructing a basis for understanding the dynamic effects of tides and wave directivity on current-based tsunami hazards in a coastal zone by the application of numerical simulation tools for hazard mapping purposes. The consideration of these aspects is crucial and yet challenging in the modeling of tsunami currents.