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 [(C₆₆ − C₄₄) ∕ C₄₄] = 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 C₆₆ is the modulus for a horizontally polarized and horizontally traveling S-wave (perpendicular to the symmetry axis), C₄₄ 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.

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

See related terms: epsilon (ε),  delta,  eta (η)