NUMERICAL MODELING OF STRONG GROUND MOTION USING 3DGEO-MODELS

摘要

A procedure for an accurate computation of seismic waveforms in large-scale three-dimensionalgeomodels is presented. The procedure is based on the numerical modeling of the seismic wavespropagation by means of a parallel implementation of the staggered grid Fourier pseudo-spectral method(FPSM). The adoption of FPSM is especially useful in addressing three-dimensional problems, because itrequires a comparatively coarser sampling of the spatial domain. The considerable saving of the computermemory makes feasible an accurate description of the attenuation effects by means of the standard linearsolid (SLS) model, which requires several variables defined over the computational domain. A furtherimprovement of the computational efficiency is obtained by using Perfectly Matching Layer (PML)absorbing boundaries whereas accurate free surface condition are implemented at the top of the model.Thanks to the parallel implementation, we are able to model the seismic wave propagation in very large3D geomodels, extending some hundreds of minimum wavelengths in each direction.The finite seismic source effects are reproduced by a cinematic model of the rupture propagation along afault plane. The planar source is simulated by summation of point sources distributed along a plane.A validation with a reference method used for horizontally layered media has been carried out for amagnitude M=6 earthquake test case ( the main shock of September 26, 1997, Umbria-Marche (Italy)event). An example is given, in which we improve the fit between the synthetic and the observedaccelerogram by introducing a 3D heterogeneity in the structural model.