Simulating Earthquake Ground Motion in 3D Structural Models with Topography Using the Fourier Pseudo-Spectral Method on Staggered Grids

Abstract eng:
We present a 3-D seismic modelling procedure, based on the Fourier pseudo-spectral method (FPSM) on structured rectangular staggered grids, which allows for an accurate modelling of the earthquake ground motion by considering the heterogeneities in the structural model (e.g. a sedimentary basin), the intrinsic attenuation of the medium, the possible irregular surface topography and a kinematical earthquake source model. The intrinsic attenuation is implemented by means of the generalized Zener body (GZB) mechanical model [1]. Irregular topography is approximated by a staircase of cubic cells and treated using an original approach based on discrete Fourier transforms of arbitrary length [2]. Sharp impedance contrasts in the structural model are handled by suitable averaging of the material properties to reduce phase misalignments and staircase effects due to the structured grid [3]. Absorbing boundaries based on the convolutional perfectly matching layer technique are adopted [4]. The efficiency of the proposed procedure is illustrated by a number of accuracy tests and examples of application on different scales, from the evaluation of local site effects in the high frequency band to the computation of the seismic response of deep sedimentary basins in the long period band. Accuracy issues in the application of 3-D seismic modelling methods for the prediction of the earthquake ground motion are discussed. An analysis of the computing performance of the parallel implementation of the procedure is also performed: it evidences that the technical issues which limited the popularity of FPSM - despite its theoretical advantages - in the early years of 3-D seismic numerical modelling, are much less critical today, thanks to the recent improvements in the multi-processor computer technology.

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