## Moveout approximations for P waves in media of monoclinic
and higher anisotropy symmetries

**Veronique Farra** **&**
**Ivan Psencik**
### Summary

We derive and test approximate P-wave moveout formulae for monoclinic,
orthorhombic or transversely isotropic media with a vertical or
horizontal axis of symmetry underlaid by a horizontal reflector
coinciding with a symmetry plane. For the derivation of the formulae,
we use the weak-anisotropy approximation, in which deviations
of anisotropy from isotropy are assumed to be small. Derived
traveltime formulae represent an expansion of traveltime with respect
to small parameters characterizing the mentioned deviations.
In addition to the traveltime formulae, we also present approximate
formulae for normal moveout velocities. All resulting formulae are
relatively simple, transparent and described by a reduced number
of weak-anisotropy parameters specifying the medium. In monoclinic,
orthorhombic or transversely isotropic media, the traveltime formulae
depend on 8, 5 or 2 weak-anisotropy parameters. The accuracy of
the formulae depends strongly on deviations of ray- and
phase-velocity directions. Nevertheless, relative traveltime errors
of the most accurate moveout formula do not exceed 1% for
anisotropies whose strength is around 25%.

### Whole paper

The paper is available in
PDF (260 kB).

*Seismic Waves in Complex 3-D Structures*, **24** (2014), 35-58
(ISSN 2336-3827, online at http://sw3d.cz).