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On the basis of the idea of migration dephasing,
the effect of the parabolic approximation of the exact one-way
wave equation is explained as undermigration
and the effect of the Crank-Nicolson numerical method that is
used to solve the diffraction equation is explained as overmigration.
The modified wave equation that the numerical
solution actually satisfies for the parabolic diffraction wave equation shows
that the trace spacing interval plays a larger role than
the depth step size of downward continuation
in determining the accuracy of the numerical solution.

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Stanford Exploration Project

11/17/1997