## Local determination of WA parameters from qS waves

**Ivan Psencik** **&**
**Xuyao Zheng**
### Summary

An algorithm for local evaluation of weak anisotropy (WA) parameters
from measurements of slowness vector components and/or of particle
motions of *qS* waves at individual receivers in a borehole in
a multi-azimuthal multiple-source offset VSP experiment is proposed.
The formulae are derived under assumption of weak but arbitrary
anisotropy of the medium and under assumption that the two *qS* waves
can be recorded separately. In contrast to *qP*-wave inversion, in which
knowledge of a single component of the slowness vector is sufficient for
performing an inversion in a medium with an arbitrary overburden, when
using *qS* waves, two components of the slowness vector or an additional
information must be available. On the other hand, use of *qS*-wave data
alone or together with *qP*-wave data may lead to the determination
of complete set of 21 WA parameters specifying the medium. General
inversion equations are specified for the case of a walkaway experiment.
Preliminary results of application of these equations to the walkaway
VSP data collected in the Java Sea region are presented.

### Keywords

Local inversion, *qS* waves, slowness vector, polarization vector,
weak anisotropy, walkaway VSP

### Whole paper

The paper is available in
PostScript (535 kB)
and GZIPped PostScript (140 kB).

In: Seismic Waves in Complex 3-D Structures, Report 12,
pp. 19-34, Dep. Geophys., Charles Univ., Prague, 2002.

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