Abstract

Over the last few years, migration-velocity analysis methods have been developed for 2-D and 3-D models by extending the assumptions and approximations used for rms velocity models. Computational requirements for these analyses have increased dramatically because top-down layer-stripping migration is needed to derive interval velocities directly instead of using rms velocities and then converting into interval velocities. We establish exact equations for 1-D and 2-D residual velocity analysis in the depth-plane-wave domain and use these in an iterative and interactive migration velocity analysis program. The new method updates interval velocities directly in a top-down residual-difference correction for all layers after prestack depth migration instead of top-down layer-stripping migration followed by residual analysis. This makes the new method a suitable tool for migration velocity analysis, especially for 3-D surveys. We test the method on synthetic and field data. The field data results show that a reasonable velocity model is obtained and most common image gathers are correctly imaged using no more than four iterations.

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