## P-wave reflection-moveout approximation
for horizontally layered media
of tilted moderate orthorhombic symmetry

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

An approximate nonhyperbolic P-wave moveout formula applicable
to horizontally layered media of moderate or weak orthorhombic
or higher anisotropy symmetry of arbitrary orientation is presented
and tested. Weak-anisotropy approximation is used for its derivation,
in which the square of the reflection traveltime is expanded in terms
of weak-anisotropy (WA) parameters specifying the anisotropy of
the layers. Due to it, the proposed formula is applicable to any offset.
Its accuracy decreases with increasing strength of anisotropy.
The relation between traveltimes and WA parameters in the formula is
transparent and relatively simple. Along a chosen single surface
profile, the formula depends in each layer on its thickness,
on the auxiliary reference P-wave velocity, on, at most,
six WA parameters describing P-wave orthorhombic or transverse isotropy
symmetry, and on three Euler angles specifying the orientation
of symmetry elements in the layer. Performed tests indicate that
the maximum relative traveltime error does not exceed 2.5% for P-wave
anisotropy about 25%. For most offsets, however, the errors are
considerably lower.

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*Seismic Waves in Complex 3-D Structures*, **29** (2019), 7-17
(ISSN 2336-3827, online at http://sw3d.cz).