Numerical Simulation Of Seismic Wave Propagation In Anisotropic Media And Fluid-solid Media By Curvilinear Grid Finite Difference Method

In seismology and its related disciplines,finite difference method(FDM)is a powerful tool for numerical simulation of seismic wave propagation in complex media;Because of its easy implementation and high computation efficiency,it has been widely used in the areas of seismic prospecting,strong ground motion,full waveforms inversion,seismic anisotropy and synthetic waveforms.In conventional FDM,rectilinear grids are used to discrete the computing space and hence the topographic free surface is described by staircase approximation which would lower the computing accuracy and lead to spurious diffractions.Although improvement methods of rectilinear grid are introducing,their applicability should be further investigated.In the proposed curvilinear grid FDM,the topographic free surface is discretized by body-conforming grids which can not only avoid the spurious waves caused by staircase approximation but also help implement free surface boundary condition correctly.Numerical simulation of seismic wavefield propagation is a basic tool for the studies of seismic anisotropy which is important to seismic exploration and earth-quakes.The staggered grid center difference scheme of the conventional FDM is highly efficient for seismic wave modeling in isotropic media;but when it comes to generally anisotropic media,the staggered grid FDM requires extra interpolations which would lower the overall accuracy of anisotropic wavefields.The collocated grid DRP/opt MacCormack scheme in the proposed curvilinear grid FDM can not only maintain the accuracy of anisotropic wavefields but also cope with body-conforming grids and traction imaging method to correctly study the effects of complex free surface on anisotropic wavefields.Correct simulation of seismic wavefields across the complex fluid-solid inter-face can help better understand the seismic data obtained from multi-component seismic ocean acquisition,and investigate the physical phenomena associated with the interface,such as the generation and propagation of the T-waves,Scholte and leaky Rayleigh waves and seismic scattering caused by seafloor.Conventional FDM can not study seismic wave across complex fluid-solid interface with accura-cy because of its approximate treatments of fluid-solid interface conditions.The proposed curvilinear grid FDM can describe the complex fluid-solid interface and implement its boundary condition with accuracy,and hence it can be used as a powerful tool to study the effects of complex fluid-solid interfaces on seismic waves.In this paper,the curvilinear grid FDM is extended to model seismic wave propagation in generally anisotropic media and fluid-solid interface media.Their two-dimensional and three-dimensional solutions are well validated by comparing with generalized reflection/transimission solutions and spectral element solutions.