Seismic waveform simulation with pseudo-orthogonal grids for irregular topographic models

In seismic waveform simulation, an irregular topography such as mountainous areas cannot be simplified to a flat surface. Even for marine seismic, a rough water bottom cannot be treated as a planar interface numerically. A body-fitted grid scheme will accurately present an earth model with an irregular topography. As it is a structured grid, then a simple finite difference scheme can be used as an efficient solver for waveform simulation. The pseudo-orthogonal property of grids is obtained by solving Poisson's equation. Investigation reveals that grids should have the acute angles > 67 degrees (90 degrees for completely orthogonal) and the cell-size change rate < 5 per cent, so that meshes are in a good orthogonality suitable for finite difference operation in waveform modelling. The acoustic wave equation and the absorbing boundary condition are reformulated from the physical space to the computational space. Waveform simulation and eventually tomographic inversion using a realistically complicated velocity model with a curved surface demonstrate the effectiveness of developed technology that works for irregular topographic models.