Seismic velocities in anisotropic media are initially derived as functions of the elastic moduli. But they may be re-formulated in terms of two reference velocities, plus several (many?) non-dimensional combinations of the moduli. If these combinations reduce to zero in the degenerate case of isostropy, they may be called anisotropic parameters. There are several ways to do this .
In the case of weak anisotropy, those relevant to a particular problem (e.g. P-wave reflections) are all much less than 1.
- Thomsen, L., 1986. Weak Elastic Anisotropy, Geophysics, 51(10), pp. 1954-1966.
- Jech, J. and I. Pšenčik, 1989. First-order perturbation method for anisotropic media, Geoph. J. Intl., 99(2), pp 369–376.