## Local inversion for anisotropy
from qP-wave slowness and polarization vectors

**Ivan Psencik** ** , **
**Xuyao Zheng** ** , **
**Steve Horne** ** & **
**Scott Leaney**
### Summary

Data from multi-azimuthal walkaway VSPs are very useful for
detection and determination of local anisotropy at individual
receivers in a borehole. Various inversion techniques have been
proposed. They differ by assumptions about properties of the
medium surrounding receivers, by types of waves involved and by
computational methods used for the inversion. We present a
technique based on the first-order perturbation theory for
anisotropic media. Basic equations of our technique are applicable
to the data of *qP* waves propagating in laterally inhomogeneous,
weakly anisotropic media of arbitrary symmetry. The data are
components of polarization and slowness vectors of *qP* waves
generated at surface sources and recorded at a given receiver. For
each source, we thus have an equation. The SVD algorithm is used
to solve an overdetermined system of equations for weak anisotropy
(WA) parameters. From them *qP*-wave phase velocity can be
reconstructed. We test the technique on a set of synthetic
multi-azimuthal walkaway VSP data and on a set of walkaway VSP
data measured in the Java Sea region. In the former case, true
anisotropy of the model is known, in the latter case, the results
of inversion can be compared with results of other techniques. In
both cases good agreement is found.

### Whole paper

The manuscript is available in
PostScript (335 kB),
GZIPped PostScript (110 kB),
and PDF (168 kB).

*Expanded Abstracts of 7th Int. Congress of SBGf (Salvador)*,
Brazilian Geophysical Society, 2001, submitted.

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