Image Differencing and Focusing in Wave-Equation Velocity Analysis

We describe a methodology for updating velocity models for depth imaging based on one-way wavefield extrapolation. The method uses an objective function that optimizes focusing in the offset domain, or equivalently, gather flatness in the angle domain. We illustrate various aspects of the method with 2D synthetic and 3D data examples from an area exhibiting strong velocity contrasts due to thin carbonate layering in sediment.