Comparison of Ocean Models for Tsunami Formation and Propagation with Nearfield Sources

Given the destructive capability of a tsunami and the resulting inundation, tsunami hazard assessment is crucial for mitigating risk to coastal communities. To assess the hazard from a tsunami generated by a distant seismic source, the shallow water equations (SWE) provide an accurate and efficient model. This is largely due to the valid assumption that the ocean is in a vertically hydrostatic state after the seismic event has ceased. For a nearfield seismic source, however, this assumption may no longer be valid. To investigate this, a compressible ocean model is derived by adding a hydroacoustic component to the hydrostatic pressure. This model is then coupled to a seismic model to capture the interaction between elastic seismic waves in the ground, acoustics waves in the ocean, and the sea surface deformation that creates the tsunami as a gravity wave. The applicability of the hydrostatic assumption for a nearfield seismic source is discussed by comparing tsunami waveforms from the derived ocean model to those of the SWE model for a variety of seismic rupture patterns.