## Weak-anisotropy moveout approximations
for P waves in homogeneous TOR layers

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

We have developed approximate P-wave reflection moveout formulas
for a homogeneous
layer of orthorhombic symmetry overlying a horizontal or dipping reflector.
The symmetry planes of the orthorhombic medium in the layer
can be arbitrarily oriented.
The formulas are based on the weak-anisotropy approximation.
Thus their accuracy depends not only on the strength of anisotropy,
but also on deviations of the phase and ray velocities.
Nevertheless, the performed tests indicate
that for P-wave anisotropy of about 25%,
the maximum relative traveltime errors of the formulas do not exceed 3%.
The formulas are expressed in terms of six P-wave weak-anisotropy parameters
and three Euler angles specifying orientation
of the symmetry planes of the orthorhombic medium.
In the case of a dipping reflector,
the formulas also depend on the apparent dip angle of the reflector.

### Whole paper

The reprint can be obtained from
Ivan Psencik.

*Geophysics*, **82** (2017), WA23-WA32.