HYBRID MODELING OF P-SV SEISMIC MOTION AT INHOMOGENEOUS VISCOELASTIC TOPOGRAPHIC STRUCTURES

A new hybrid two-step method for computation of P-SV seismic motion at inhomogeneous viscoelastic topographic structure is presented. The me thod is based on a combination of the discrete-wavenumber (DW), finite -difference (FD), and finite-element (FE) methods. In the first step, the DW method is used to calculate the source radiation and wave propa gation in the background 1D medium. In the second step, the FD-FE algo rithm is used to compute the wave propagation along the topographic st ructure. The accuracy of the method has been separately tested for inc lusion of the attenuation and for inclusion of the free-surface topogr aphy through numerical comparisons with analytical and independent num erical methods. The method is a generalization of the hybrid DW-FD met hod of Zahradnik and Moczo (1996) for localized structures with a flat free surface. Numerical computations for a ridge, sediment valley, an d the ridge neighboring the sediment valley show that a ridge can cons iderably influence the response of the neighboring sediment valley. Th is means that the neighboring topographic feature should be taken into account even when we are only interested in the valley response.