Shear Wave Birefringence In Reverse VSP: An Approach To 3-D Surface P To S Converted Waves
Name
1998.6 Sierra_Queen.pdf
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412.42 KB
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Adobe PDF
Checksum (MD5)
2d6376baa153affc04f10ccef46383ce
Author(s)
Sierra, Jesus
Queen, John H.
Date Issued
1998
Publisher
Massachusetts Institute of Technology. Earth Resources Laboratory
Series/Report no.
Earth Resources Laboratory Industry Consortia Annual Report;1998-06
Abstract
We present an original method to estimate local shear wave birefringence properties for
3-D surface P to S converted waves. To accomplish this we approach the problem in
reverse VSP (RVSP), and we show that they are equivalent. The method works in the
pre-stack domain and uses the converted P to S waves as hypothetical sources to study
the problem under the propagator matrix method in transmission. The importance of
this method is that no information is required about layering above the zone of interest
to obtain an accurate estimation of the anisotropy parameters. The method involves
solving a nonlinear problem in the frequency domain where a global minimization technique
called Simulation Annealing is used. The procedure also allows us to estimate the
axis of anisotropy independently of the offset angle in the range of angles considered in
VSPs and in surface profiles. The proposed method is validated with synthetic RVSP
data for two models with different densities of vertical fractures. Results show good
accuracy in the estimation of the angle of the fractures for the whole range of offsets.
Also, results show a dependence on the frequency and offset ranges considered in the
analysis.
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