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Another attractive application of common-azimuth processing of 3-D marine
data is the possibility to perform velocity estimation based
on the focusing of wavefield at depth.
``Focusing analysis'' has been successfully applied
to estimate depth-migration velocities for 2-D data
MacKay and Abma (1992); Yilmaz and Chambers (1984).
It has some inherent advantages with respect to velocity
estimation based on coherency of migrated events across offsets,
that is the criterion routinely used in conjunction
with Kirchhoff prestack migration.
Residual moveout applied to
migrated constant-offset data is only a
partial residual focusing operator,
since it does not refocus the data along the midpoint axes.
By contrast, focusing analysis based on downward-continuation
operators does include a midpoint component.
Because of these inherent advantages,
velocity-estimation methods based on wavefield focusing,
have been revived lately and proposed for 3-D velocity
estimation as Common Focal Point (CFP) methods
Kabir and Verschuur (1996); Morton and Thorbecke (1996).
However, the straightforward application
of CFP methods to 3-D data with arbitrary geometry
could be extremely computationally intensive.
Whereas, the application of CFP methods to marine data
using the common-azimuth imaging tools described
in this paper would be computationally efficient,
and thus they could become practical methods
to estimate velocity for 3-D prestack depth imaging of
a wide class of marine data sets.

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Stanford Exploration Project

11/11/1997