Shallow water numerical models for the 1947 gisborne and 2011 Tohoku-Oki tsunamis with kinematic seismic generation

Abstract

Traditionally, the initialization of seismically generated tsunamis is done by setting the initial free surface deformation as identical to the final deformation of the sea floor. However, numerous effects are neglected through this method, in particular the dynamics of the sea floor deformation. Here, two temporal parameters characterizing the sea floor deformation are defined: the rise time tr (vertical motion) and the rupture velocity Vp (horizontal motion). These parameters have already been theoretically introduced by Hammack (1973) and Todorovska and Trifunac (2001), respectively. For a simplified and schematic motion of the sea floor using simultaneously both parameters, a theoretical linear analysis developed in Le Gal et al. (2017) showed a resonance phenomenon for which the amplitude of the generated wave becomes significantly larger than the amplitude of the sea floor deformation. This phenomenon concerns deformation with small rise times and rupture velocities close to the linear long wave velocity gh. The aim of the present study is to investigate the influence of a kinematic deformation, using both parameters, during historical tsunamis with numerical nonlinear shallow water simulations. This work corroborates Le Gal et al.’s theoretical schematic analysis. For this purpose, two events are studied: the March 1947 New Zealand and the 2011 Japan tsunamis.