Evaluating the Stolt - stretch parameter a

The Stolt migration extension to a variable velocity case describes the velocity heterogeneity with a constant parameter, which is related to the stretch transformation of the time axis. We exploit a connection between modified dispersion relations and nonhyperbolic traveltime approximations to derive an explicit expression for the stretch parameter. This analytical expression allows one two achieve the highest possible accuracy within the Stolt stretch approximation. Using a real data example, we demonstrate an application of the explicit Stolt stretch formula for an optimal partitioning of the migration velocity in the method of cascaded migrations.