Applicability of the ray theory for S-wave propagation in elastic weakly anisotropic inhomogeneous media

Vaclav Vavrycuk


Propagation of P waves in elastic, weakly anisotropic, inhomogeneous media can be studied by the ray theory without any problem. Propagation of S waves in such media, however, creates more complications in the ray theory. These complications are caused mainly by the so-called S-wave coupling. It is known that the standard zeroth-order ray theory is inapplicable, if the S-wave coupling is significant in the wavefield. In this case, modifications of the ray theory such as the coupling ray theory or the quasi- isotropic approximation of the ray theory have so far been used to reproduce the S waves correctly. We show, however, that the failure of the ray theory is not principal, and that it can be overcome even without modifying the ray theory. We show that the ray theory fails because only the zeroth-order term of the ray series is considered. If we include higher-order ray approximations in the solution, we obtain correct results. On a simple example of a plane S wave propagating in a weak transversely isotropic medium with a rotating axis of symmetry we study the accuracy of the ray theory in dependence on the number of higher-order ray approximations considered in the ray solution.

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In: Seismic Waves in Complex 3-D Structures, Report 8, pp. 127-149, Dep. Geophys., Charles Univ., Prague, 1999.
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