Stress-induced transverse isotropy in rocks

The application of uniaxial pressure can induce elastic anisotropy in otherwise isotropic rocks. We consider models based on two very different rock classes, granites and weakly consolidated granular systems. We show (1) that these models share common underlying assumptions, (2) that they lead to similar qualitative behavior, and (3) that both provide a microscopic basis for elliptical anisotropy. In contrast, a finely layered transversely isotropic medium always shows anelliptical anisotropy. In the granular case, we make experimentally verifiable predictions regarding the horizontally propagating modes based on the measured behavior of the vertical modes.