Elastic Wave Modeling and Pre‐stack Reverse Time Migration of Irregular Free‐surface Based on Layered Mapping Method

Abstract

Traditional FD method has some difficulties in treating irregular surface, while mapping method can overcome the disadvantage by transform the irregular surface to horizontal surface. But at the same time, the interface below the surface is transformed to more complex interface, resulting in the inaccurate of wave propagation and imaging. In this paper, a layered mapping method is proposed and it is applied to elastic wave RTM. This method not only can overcome the effects of irregular surface but also underground structure can not be destroyed. Wave field forward continuation, reverse time continuation and separation are completed in auxiliary system coordinate while imaging in Cartesian. Numerical examples of simple topography model and Zhongyuan topography model show the correctness of the method proposed in the paper. Meanwhile after testing two extreme cases of inaccurate interface elevation we can see that the imaging results of layered mapping RTM is much better than that of traditional mapping RTM.