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I chose here a particular example of relating velocity measurements at different
scales, namely a well log and a surface seismic data set. I have applied
Dix and Schoenberg&Muir averaging to the well log and compared it with
the surface seismic velocity analysis. Both approaches replace the overburden
with an homogeneous equivalent. However the sense of averaging is
different. Overlaying velocity analysis, Dix rms velocity and §+M
derived velocities show that Dix rms velocity seems consistently higher
(up to 15%). The §+M average gives velocities that seem closer
to the analysis picks (up to 5% deviation);
At large depths however it is noticeably off the velocity picks.
The §+M average is consistently
lower than the Dix rms average, as we would expect since the high
frequency average is based on the Fermat's principle and is thus least
travel time.

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Stanford Exploration Project

11/17/1997