ELASTIC WAVE-PROPAGATION IN MEDIA WITH PARALLEL FRACTURES AND ALIGNED CRACKS

A model of parallel slip interfaces simulates the behavior of a fracture system composed of large, closely spaced, aligned joints. The model admits any fracture system anisotropy: triclinic (the most general), monoclinic, orthorhombic or transversely isotropic, and this is specified by the form of the 3 multiplied by 3 fracture system compliance matrix. The fracture system may be embedded in an anisotropic elastic background with no restrictions on the type of anisotropy. To compute the long-wavelength equivalent moduli of the fractured medium requires at most the inversion of two 3 multiplied by 3 matrices. When the fractures are assumed on average to have rotational symmetry (transversely isotropic fracture system behavior) and the background is assumed isotropic, the resulting equivalent medium is transversely isotropic and the effect of the additional compliance of the fracture system may be specified by two parameters (in addition to the two isotropic parameters of the isotropic background). Although knowledge of the total of four parameters describing the anisotropy of such a fractured medium tells nothing of the size or concentration of the aligned fractures, it does provide information as to the overall excess compliance due to the fracture system and its orientation.