Prestack migration algorithms are relatively simple variants of the poststack methodologies. The primary difference lies not in the mathematical theory but in the way in which any given algorithm is structured and applied to recorded multi-fold data. The basic differences arise because the prestack method must handle non-coincident sources and receivers. This means that it must handle the traveltime issues and amplitude correction factors associated with the source and similar issues for each and every receiver.
To resolve this issue, it is normal to split the imaging problem into two independent pieces. One piece handles the traveltime and amplitude from the source to the image point, while the other handles the traveltime and amplitude from the image point to the receiver. When both pieces are based on the same modeling approach, the names of the prestack algorithms are frequently identical to those given to the poststack methods from which they arose. When the two pieces are based on technically different methods, the resulting algorithm is assigned a hybrid combination of the two names. Figure 1 details these methodologies and becomes the framework for the discussion on zero offset technologies.
