Tau migration and velocity analysis: Theory and synthetic examples

Prestack migration velocity analysis in the time domain reduces the velocity-depth ambiguity usually hampering the performance of prestack depth-migration velocity analysis. In prestack migration velocity analysis, we keep the interval velocity model and the output images in vertical time. This allows us to avoid placing reflectors at erroneous depths during the velocity analysis process and, thus, avoid slowing down its convergence to the true velocity model. Using a 1D velocity update scheme, the prestack τ migration velocity analysis performed well on synthetic data from a model with a complex near-surface velocity. Accurate velocity information and images were obtained using this time-domain method. Problems occurred only in resolving a thin layer where the low resolution and fold of the synthetic data made it practically impossible to estimate velocity accurately in this layer. This ID approach also provided us reasonable results for synthetic data from the Marmousi model. Despite the complexity of this model, the τ domain implementation of the prestack migration velocity analysis converged to a generally reasonable result, which includes properly imaging the elusive top-of-the-reservoir layer.