HYBRID SEISMIC MODELING BASED ON DISCRETE-WAVE NUMBER AND FINITE-DIFFERENCE METHODS

Any calculation of seismic wave propagation comprising the seismic sou rce, the travel path, and the receiver site in a single finite-differe nce (FD) model requires a considerable amount of computer time and mem ory. Moreover, the methods currently available for including point sou rces in the 2D FD calculations are far-field approximations only. Ther efore we have developed a new hybrid method for treating the seismic w ave fields at localized 2D near-surface structures embedded in a 1D ba ckground medium, and excited by a point source. The source radiation a nd propagation in the background model is solved by the discrete-wave number (DW) method, while the propagation in the local 2D structure is calculated by the FD method. The coupling between the two sets of cal culations is performed on a rectangular excitation box surrounding the local structure. We show the usefulness of the method in ground-motio n studies where both near-field source effects and local site effects are important. Technical problems connected with the inconsistency bet ween the 3D source radiation and the 2D FD calculation are minor for t he relatively distant in-plane point explosive sources, but are more s erious for the in-plane dislocation sources.