[S-SS07] Seismic wave propagation: Theory and Application

[SSS07-P01] Surface gravity approximation for calculation of nearfield tsunami and seismic waves by the reflectivity method

*Hiroshi Takenaka¹, Tomotsugu Watanabe¹, Takeshi Nakamura² (1.Department of Earth Sciences, Okayama University, 2.Central Research Institute of Electric Power Industry)

Keywords:nearfield tsunami, seismic wave, discrete wavenumber method

Around near-fault area under the sea the seawater motion associated with tsunami generation immediately follows the sea-bottom seismic motion, permanent sea-bottom deformation and ocean acoustic waves. We have developed a quasi-analytical method for calculating full motion on and above the sea bottom due to nearfield seismic wave propagation and tsunami wave generation and propagation for horizontally stratified media with compressible water layers on top of a multi-layered solid half-space, where the method introduced the gravitational effect into the seawater layer to excite tsunami waves. The solution method is based on the Kennett and Kerry's (1979) reflection/transmission matrices and Bouchon's (1981) discrete wavenumber summation method. We here propose a good approximation to incorporate tsunami-associated wavefield into seismic wave synthesis with the reflectivity method, instead of the strict method we previously developed. It may be the simplest way to implement the tsunami generation in a usual reflectivity code for seismic wave calculations, which only replace the water surface reflection coefficient (i.e. -1) in the reflectivity code by the reflection coefficient for the free surface of a gravitational fluid. We call this approximation "surface gravity approximation." We also show the accuracy of this approximation in our presentation.

Bouchon, M. (1981). A simple method to calculate Green's functions for elastic layered media. Bulletin of the Seismological Society of America, 71(4), 959-971.

Kennett, B. L. N. and N. J. Kerry (1979). Seismic waves in a stratified half space. Geophysical Journal of the Royal Astronomical Society, 57(3), 557-583.