Seismic Modeling And Reverse-time Migration With A Finite-difference Method On Irregular Grids

A new finite-difference method is developed for seismic modeling and reverse-time migration based upon the Voronoi Cell construction on irregular grids. Curved velocity boundaries and irregular earth surface can be accurately represented using the irregular grid implementation. Therefore the modeled and migrated results can be more accurate, and meanwhile, the efficiency is still preserved using an explicit finite-difference scheme.The details of the construction and characteristics of the new finite-difference scheme are presented in this thesis, by using both the integration theorem and the Taylor expansion theory. It is proved that the new approach has the second-order accuracy on the grids with axis-symmetric Voronoi Cells and at least has the first-order accuracy in general. According to this character of the scheme and the computational requirements of the finite-difference approach, a striping procedure is involved to decompose the velocity model into variable spatial size grids with a nearly constant tune step preserved. Compared with the conventional finite-difference method on the fixed grid-size rectangular grids, the new method can be more cost-effective in complex models.Numerical tests for both seismic modeling and reverse-time migration are performed on various theoretical models and a physical experiment. The test results demonstrate that this new finite-difference method can be efficient and sufficiently accurate. It may also be an effective and robust tool in other areas involving the numerical computation of partial differential equations.