Commonly used quasi-isotropic approximations of the coupling ray theory are discussed. The coupling ray theory and its quasi-isotropic approximations are then numerically compared with the exact analytical solution for the plane S wave, propagating along the axis of spirality in the 1-D anisotropic "oblique twisted crystal" model.
Coupling ray theory, quasi-isotropic approximation, seismic anisotropy, travel time, amplitude, Green function.
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