There is no reciprocity in the arrival times for P-S reflections, i.e., arrival times are different if the locations of the shot and geophone are exchanged. For P-S reflections in CMP panels, this results in terms in the arrival times [t(x)] which are linear in offsets (x). The principle of reciprocity still holds if the medium is laterally homogeneous and the reflectors are horizontal. For a laterally homogeneous-earth model, with a nonhorizontal reflector, the analysis of t(x) curves for P-S arrivals, particularly for terms linear in x, provides new opportunities for obtaining information about local (near the reflector) velocities and velocities which have been averaged over depth.If there is a dipping reflector (or if there is a lateral variation of earth parameters) the coincident shot-geophone P-S reflection does not correspond to the normal incident angle. Therefore, for coincident locations of the shot and geophone, there exists a converted S-wave of nonzero amplitude.

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