3-D prestack depth migration and residual picking in common image gathers (CIGs) are the most timeconsuming part in 3-D migration velocity analysis. We propose a new algorithm that provides 3-D velocity analysis quickly and accurately. Spatial coordinates and orientations of reflection points are provided by 3-D poststack or prestack parsimonious migration; the migration involves only time samples that are picked from the salient reflection events on a poststack volume or on one common-offset volume. Ray tracing from the reflection points to the surface provides a common-reflection point (CRP) gather for each reflection point. Predicted moveouts for local velocity perturbations, based on the maximizing stacked amplitude, gives the estimated velocity updates for each CRP gather. The traveltime picking is limited to only a stacked or common-offset volume, and it needs to be done only once; there is no need to do intensive 3-D prestack depth migration. Hence, the computation is much faster than other migration-based velocity analyses. 3-D synthetic data tests show the algorithm works effectively and efficiently.

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