We propose a method for estimating interval velocity using the kinematic information in diffractions. We extract velocity information from migrated diffracted events by analyzing their residual focusing in physical space (depth and midpoint) using prestack residual migration. The results of this residual-focusing analysis are fed to a linearized inversion procedure that produces interval velocity updates. Our inversion procedure employs a wavefield-continuation operator linking perturbations of interval velocities to perturbations of migrated images, based on the principles of Wave Equation Migration Velocity Analysis (WEMVA) introduced in recent years. We measure the accuracy of the migration velocity by using a diffraction-focusing criterion, instead of the criterion of flatness of migrated common-image gathers that is commonly employed in Migration Velocity Analysis (MVA). This new criterion enables us to extract velocity information from events that would be challenging to use with conventional MVA methods, and thus makes our method a powerful complement to conventional MVA methods. We demonstrate our method with synthetic and real Ground-Penetrating Radar data.