Overview

This chapter presents a migration velocity analysis (MVA) method based on wavefield extrapolation. Similar to conventional MVA, this method aims at iteratively improving the quality of the migrated image, as measured by flatness of angle-domain common image gathers over the aperture angle axis. However, instead of inverting the depth errors measured in ADCIGs using ray-based tomography, I invert ``image perturbations'' using a linearized wave-equation operator. This operator relates perturbations of the migrated image to perturbations of the migration velocity. I use prestack Stolt residual migration to define the image perturbations that maximize focusing and flatness of ADCIGs.

The linearized velocity analysis operator relates slowness perturbations to image perturbations based on a truncation of the Born scattering series to the first order term. To avoid divergence of the inversion procedure when the velocity perturbations are too large for the Born linearization of the wave-equation, I do not invert directly the image perturbations obtained by residual migration, but a linearized version of those image perturbations. The linearized image perturbations are computed by a linearized prestack residual migration operator applied to the background image.