An S-wave parameter for a medium in which the elastic properties exhibit vertical transverse isotropy. Gamma (γ) is the S-wave anisotropy parameter and is equal to half the ratio of the difference between the horizontally and vertically traveling SH-wave velocities squared divided by the vertically traveling SH-wave velocity squared; an SH-wave is a shear wave that is horizontally polarized.

γ ≡ ½ [(C_{66} − C_{44}) / C_{44}] = ½ [(V_{SH⊥}^{2} − V_{SH∥}^{2}) / V_{SH∥}^{2}]

S-wave parameter (γ) for a medium in which the elastic properties exhibit vertical transverse isotropy, where C_{66} is the modulus for a horizontally polarized and horizontally traveling S-wave (perpendicular to the symmetry axis), C_{44} is the modulus for a horizontally polarized and vertically traveling S-wave (parallel to the symmetry axis), V_{SH}_{⊥} is the velocity for a horizontally polarized and horizontally traveling S-wave and V_{SH}_{∥} is the velocity for a horizontally polarized and vertically traveling S-wave.