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Articles |
Department of Geosciences, State University of New York at Stony Brook, Stony Brook, NY 11794-2100, USA (e-mail: Teng-fong.Wong{at}stonybrook.edu)
The elastic properties of a cracked rock are transversely isotropic if its crack density distribution is axisymmetric. The three Thomsen parameters
, 
and 
are used to characterize the seismic properties of a weakly anisotropic rock. In this study we calculated these anisotropy parameters in such a cracked rock under dry and saturated conditions. We derived analytic expressions for a dry rock based on an approximate model proposed by earlier workers, which shows elliptically anisotropic behaviour. Guided by microstructural observations we adopted a two-parameter axisymmetric distribution to characterize the crack density, which predicts that in a fluid-saturated rock the parameters and are related to in a nonlinear manner. All three parameters considered are sensitively dependent on the difference in the densities of cracks with normals parallel and perpendicular to the symmetry axis. Theoretical predictions of the model are compared with laboratory and field measurements of seismic anisotropy.
