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This chapter
presents a migration velocity analysis (MVA) method
based on wavefield extrapolation.
Similar to conventional MVA, this method aims at iteratively
improving the quality of the migrated image,
as measured by flatness of
angle-domain common image gathers
over the aperture angle axis.
However,
instead of inverting the depth errors measured in ADCIGs
using ray-based tomography,
I invert ``image perturbations'' using
a linearized wave-equation operator.
This operator relates
perturbations of the migrated image to
perturbations of the migration velocity.
I use prestack Stolt residual migration
to define the image perturbations that
maximize focusing and flatness of ADCIGs.
The linearized velocity analysis operator relates
slowness perturbations to image perturbations
based on a truncation
of the Born scattering series to the first order term.
To avoid divergence of the inversion procedure
when the velocity perturbations are too large
for the Born linearization of the wave-equation,
I do not invert directly the image perturbations
obtained by residual migration,
but a linearized version of those image perturbations.
The linearized image perturbations are computed
by a linearized prestack residual migration operator
applied to the background image.

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Stanford Exploration Project

11/4/2004