The presented approximate formulas yield a critical value of anisotropy parameter sigma, for which an incipient off-axis SV-wave triplication occurs in transversely isotropic media. The formulas are simple and approximate the exact solution with a high accuracy. The best results are obtained by the third-order approximation, which yields accuracy at least 20 times higher than the formulas presented by Thomsen & Dellinger (2003). The formula works safely for parameters kapa=a33/a44 .GT. 2 and 0.2 .GT. epsilon=(a11-a33)/2a33 .GT. -0.2 yielding critical values of sigma from 0.1 to 0.7. Out of this interval, it is recommended to use an exact solution.
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