Abstract:

Seismic wave modeling in frequency-space domain is the foundation of full waveform inversion in frequency and Laplace-Fourier domain. An accurate seismic wave modeling with surface topography is the kernel of full waveform inversion which can direct process data recorded on relief surface. Based on acoustic wave equation with PML absorption boundary condition, the free surface condition on relief surface is included into the optimized 9-points finite difference algorithm in frequency space domain. Then the variable grid method which refines the grid near the surface and remains the rest unchangeable is introduced to increase the computational efficiency and decrease the memory cost. The theoretical analysis and numerical test show that: 1) the diffraction caused by grid discretization of the relief surface can be suppressed by refining the grid; 2) through the variable grid method, computational efficiency can be improved for several times and the memory cost can also be decreased for several times easily; 3) the energy of artificial reflection caused by the boundary of fine and coarse grid is less than 2% of the energy of the original  wavefield which is acceptable for the seismic wavefield modeling and inversion.

Key words: surface topography, variable grid, frequency domain, numerical modeling