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Diffracted events contain useful velocity information
that is overlooked by conventional MVA methods,
which use flatness of common image gathers as the only criterion
for the accuracy of migration velocity.
In this section, I demonstrate that accurate interval-velocity updates
can be estimated by inverting the results of a residual-focusing analysis
of migrated diffracted events.
To convert residual-focusing measurements into interval-velocity updates,
I employ the WEMVA methodology (wemva) which
is ideally suited for this task
because it is capable of inverting image perturbations directly,
without requiring an estimate of the reflector geometry.
In contrast, ray-based MVA methods require
the reflector geometry to be provided by interpreting the migrated image.
However, since the interpretation of partially-focused
diffracted events is an extremely difficult task,
ray-based methods are never employed for diffraction-focusing
velocity analysis.
The seismic-data example demonstrates how
the WEMVA method can exploit the velocity information contained
in the event generated by a rugose salt-sediment interface.
This kind of events is present in many salt-related data sets,
and the ability of using the diffracted energy to
further constrain the velocity model might significantly
improve the final imaging results.
The GPR-data example demonstrates the significant potential of the
WEMVA method for improving the imaging of GPR data.
I demonstrate that the interval-velocity model
obtained by extracting velocity information from the diffracted events
improves the reflector continuity in the migrated image
and facilitates geological interpretation of the images.
Since a large number of GPR data sets are limited to zero-offset data,
the possibility of using diffractions to define the lateral variations
in interval velocity can substantially widen the range of applications
of GPR methods.
Next: Conclusions
Up: Diffraction-focusing WEMVA example
Previous: Imaging of GPR data
Stanford Exploration Project
11/4/2004