We introduce a new partial-migration operator, named Azimuth Moveout (AMO), that rotates the azimuth and modifies the offset of 3-D prestack data. AMO can be effectively applied to improve the accuracy and to reduce the computational cost of 3-D prestack imaging. For example, a 3-D prestack dataset can be drastically reduced in size by coherent partial-stacking after AMO. The reduced dataset can be then imaged by prestack depth migration, a process that would have been too expensive to apply to the original dataset. AMO can also be effectively used for regularizing data geometries (e.g. correct for cable feather) and for interpolating unevenly sampled data.
AMO is defined as the cascade of DMO and inverse DMO at different offsets and azimuths. We derive the time-space domain formulation of the AMO operator by first deriving its Fourier domain representation, and then analytically evaluating the stationary-phase approximation. The impulse response of AMO is a surface in the time-midpoint space; the shape of the surface is a skewed saddle, and its spatial extent is determined by the amount of azimuth rotation and offset continuation to be applied to the data. When the azimuth rotation is small (i.e; less than 20 degrees), the AMO operator is compact and inexpensive to apply in the time-space domain. We successfully tested AMO by coherently stacking traces with similar offsets and azimuths from a synthetic land survey.