**1. n. [Geophysics]**

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}*

Reference: Thomsen L: “Weak Elastic Anisotropy,” *Geophysics *51, no. 10 (October 1986): 1954–1966.

**See:**
epsilon (ε),
delta,
eta (η)

Vertical transverse isotropy.