Shear-induced conversion of seismic waves across single fractures

Elastic wave conversions across a fracture in rock subjected to shear stress are observed during laboratory ultrasonictransmission tests. Compressional waves (P-waves) and shear waves (S-waves) normally incident on a sheared fracture are partially converted to waves with particle motions that are not present in the incident waves. The amplitudes of the converted waves increase significantly with increasing shear stress applied to the fracture. The particle motion of the converted wave changes its phase by 180 degrees when the direction of the sheer is reversed. These wave behaviors can be explained by adding the coupling (dilational) components in the fracture stiffness matrix of the displacement-discontinuity boundary conditions for a non-welded interface. The shear-induced wave conversion presented in this paper has a wide range of potential applications for monitoring and determining the magnitude of shear stress acting on fractures in geologic and engineered materials. (C) 2000 Elsevier Science Ltd. All rights reserved.