| Seismic wavefield modeling is an important tool for the study of seismic wave-form inversion, strong motion prediction, seismic imaging and properity of seismic wavefield. The convnetional analytical or semi-analytical solutions (such as FK method, Cagniard-de Hoop method, generalized reflection/transmission method)for seismic wavefield modeling can only deal with flat interface media models with high accuracy but they can not handle the complex media models. Numerical methods (such as fintie difference method (FDM), pseudospectral method, finite element method, spectral element method) demend more computing resources than the conventional analytical or semi-analytical solutions, whereas they can deal with complex media models by discretizing the seismc wave equations. With the development of computer science, numerical methods have been the dominant tools for seismic wavefield modeling.In comparison with other nuemrical methods, FDM is easy in algorithm and griding, and fit for parallel computing; hence it has been widely used in seismic prospecting and engineering. The study of free surfce boundary condition im-plementment in FDM is an important technique for seismic wavefield modeling in complex media. In this dissertation, we summary previous studies on the im-plementment of free surface boundary condition in FDM; and then validate five stable algorithms and give comparsions of the five methods in term of accuracy. |
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