The standard anisotropic ray theory does not work properly or even fails when applied to S-wave propagation in inhomogeneous weakly anisotropic media or in the vicinity of shear-wave singularities, where the two shear waves propagate with similar phase velocities. The coupling ray theory was proposed to avoid this problem.
In it, amplitudes of the two S waves are computed by solving two coupled, frequency-dependent differential equations along a common S-wave reference ray. In this paper, we test two recently developed algorithms of the coupling ray theory.
As a reference, we use the Fourier pseudo-spectral method, which does not suffer from limitations of the ray methods and yields very accurate results