Prestack Kirchhoff migration (KM0 is computation- ally intensive for iternative velocity analysis. This is partly because each time sample in a trace must be smeared along a quasi-ellipsoid in the model. As a less costly alternative, we used the stationary phase approximation to the KM integral so that the time sample is smeared along a small Fresnel zone portion o the quasi-ellipsoid. This is equivalent to smearing the time samples in a Trace over a 1.5-D fat ray (i.e., wavepath), so we call this "wavepath migration" (WM).
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