High precision numerical simulation of the trans-pacific tsunami caused by the 2011 Tohoku earthquake

Abstract:

For high-precision simulations of the trans-pacific tsunamis, we would have to include additional effects on the conventional long-wave theory. Water waves with different wavelengths travel at different speeds so that frequency dispersion is not negligible in the far-field tsunamis. It can be modelled with Boussinesq equations. Baba et al. (2015) developed a high-speed code solving the Boussinesq equations. Recently, importance of effects of small elastic deformation of the Earth loaded by tsunami and seawater density vertical stratification were shown in many studies for the 2010 Chile and 2011 Tohoku far-field tsunamis. Allgeyer and Cummins (2014) successfully suggested a practical method to add these effects in the conventional numerical scheme. However, we don’t have yet a simulation code the all effects incorporated simultaneously. This study combined the module of Allgeyer and Cummins (2014) with the Baba’s (2015) code. Also here the elastic loading model was improved by considering the gravitational potential change during the tsunami propagation. Calculation with these all effects incur a huge computational cost, so we used a high performance vector computer, Earth Simulator 3, installed in JAMSTEC this year. With the new code on the new computer, we simulated the trans-pacific tsunami by giving a time-dependent sea surface development during the 2011 Tohoku earthquake estimated by the multi-time window tsunami inversion method that used dispersive Green’s functions. Our calculation provided a good agreement with the deep-ocean observations at the whole Pacific Ocean. We also found that the three effects, Boussinesq, elastic loading and sea water stratification are equally important simulating the tsunami waveforms in far-field.