Depth-focusing analysis (DFA) is a method of prestack velocity estimation that relies on the interpretation of amplitudes at zero offset to determine the extrapolation depth that best focuses the data. The interpreted focusing depths may then be used to update the migration-velocity field for the next iteration of migration. Unfortunately, seismic energy from dipping interfaces, diffractions, and noise often produce spurious amplitude indications of focusing that can hinder the DFA interpretation proces. Therefore, we introduce a new method of determining focusing that is relatively independent of amplitude. Our approach is based on measures of normal moveout derived from nonzero-offset data saved during migration. By relating steeper moveout to smaller radius of wavefront curvature, focusing may be defined by a wavefront curvature of zero radius. Finally, the application of inverse-radius weights to the amplitude data is shown to attenuate non-focused events due to their large radius of curvature.


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