Getting a good image by stacking after normal moveout (NMO) correction and/or after prestack migration requires reasonably flat gathers. Amplitude variation with offset (AVO) studies on prestack data require flat gathers after NMO. Otherwise slope and intercept attributes get contaminated. When the raypath of the seismic energy includes inhomogeneities, NMO algorithms based on flat layer assumptions, even prestack time migration, may fail to produce flat gathers (Figure 1). Such gathers may require a robust, brute force, gather flattening method.

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