PS-wave moveout in anisotropic media of arbitrary symmetry and tilt

Veronique Farra & Ivan Psencik

Summary

As previous studies of reflection moveout show, use of unconverted P waves leads to formulae, which relate the moveout to only a limited number of parameters specifying anisotropy. Use of converted PS waves extends the number of parameters to, generally, complete set of twenty one parameters. We present and test an approximate formula for the reflection moveout of a wave converted at a horizontal reflector underlying a homogeneous layer of arbitrary anisotropy symmetry. For its derivation, we use the weak-anisotropy approximation. It leads to an approximate formula for the square of the reflection traveltime expressed in terms of A-parameters, parameters used to specify anisotropy. The complete set of A-parameters represents an alternative to twenty one independent elements of the stiffness tensor. Traveltimes are calculated along reference rays of converted reflected waves traced in a reference isotropic medium. Presented tests indicate that the maximum relative traveltime errors are less than 1% for models with P- and S-wave anisotropy of less or slightly higher than 10% and less than 2% for models with P- and S-wave anisotropy of less or slightly higher than 20%, respectively.

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Seismic Waves in Complex 3-D Structures, 31 (2022), 31-54 (ISSN 2336-3827, online at http://sw3d.cz).