Wave-equation migration velocity analysis — II: Subsalt imaging examples Geophysical Prospecting, accepted for publication Paul Sava and Biondo Biondi Stanford Exploration Project, Mitchell Bldg., Department of Geophysics, Stanford University, Stanford, CA 94305-2215 (July 22, 2004) ABSTRACT Subsalt imaging is strongly dependent on the quality of the velocity model. However, rugose salt bod- ies complicate wavefield propagation and lead to subsalt multipathing, illumination gaps and shadow zones which cannot be handled correctly by conventional traveltime-based migration velocity anal- ysis. We overcome these limitations by the wave-equation migration velocity analysis technique introduced in a companion paper (Sava and Biondi, 2004) and demonstrate the methodology on a re- alistic synthetic dataset simulating a salt dome environment and a Gulf of Mexico dataset. We model subsalt propagation using wavepaths created by one-way wavefield extrapolation. Those wavepaths are much more accurate and robust than broadband rays, since they inherit the frequency dependence and multipathing of the underlying wavefield. We formulate an objective function for optimization in the image space by relating an image perturbation to a perturbation of the velocity model. The image perturbations are defined using linearized prestack residual migration, thus ensuring stability relative to the first-order Born approximation assumptions. Synthetic and real data examples demonstrate that wave-equation MVA is an effectivetool for subsalt velocity analysis, even when shadows and illumination gaps are present. 1