Three-dimensional ray tracing in <i>P</i>-wave azimuthal anisotropic media

SUMMARY A new 3-D ray-tracing method is developed for P-wave azimuthal anisotropic (AAN) media. We assume anisotropic media with hexagonal symmetry and take advantage of the property that the AAN symmetry axis, the phase velocity vector and the group velocity vector are located in the same plane. The 3-D ray-tracing method that combines the pseudo-bending technique and Snell's law is improved for the AAN media. We compute isotropic (ISO) and AAN rays in synthetic models and an actual 3-D P-wave AAN model of the East Japan subduction zone. The accuracy of our ray-tracing code is evaluated by comparing the ray-path and travel-time differences between the ISO and AAN rays. Our results show that the AAN rays in each model bend in the right direction and satisfy Fermat's principle, so the theory and approximations adopted in the calculations are reasonable. For long rays (&amp;gt;350 km), the ray-path difference between the ISO and AAN rays is &amp;gt; 20 km, and the travel-time difference is &amp;gt; 0.1 s, suggesting that it is necessary and important to take azimuthal anisotropy into account in the 3-D ray tracing.