The common ray approximation considerably simplifies the numerical algorithm of the coupling ray theory for S waves, but may introduce errors in travel times due to the perturbation from the common reference ray. At present, the common reference rays are routinely represented by the isotropic common rays calculated in the isotropic reference model, but they would better be represented by the anisotropic common rays calculated in the anisotropic model. The errors due to the anisotropic common ray approximation of the coupling ray theory are usually considerably smaller than the errors due to the routinely used isotropic common ray approximation of the coupling ray theory.
We numerically calculate the travel-time errors due to the anisotropic common ray approximation in three 1-D models of differing degree of anisotropy, and compare them with the errors due to the isotropic common ray approximation. The differences between the isotropic and anisotropic common ray approximations of the coupling ray theory are demonstrated on synthetic seismograms.
Coupling ray theory, common ray approximation, travel time, seismic anisotropy, inhomogeneous media.
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