FRACTURE INTERFACE WAVES

Interface waves on a single fracture in an elastic solid are investiga ted theoretically and numerically using plane wave analysis and a boun dary element method. The finite mechanical stiffness of a fracture is modeled as a displacement discontinuity. Analysis for inhomogeneous pl ane wave propagation along a fracture yields two dispersive equations for symmetric and antisymmetric interface waves. The basic form of the se equations are similar to the classic Rayleigh equation for a surfac e wave on a half-space, except that the displacements and velocities o f the symmetric and antisymmetric fracture interface waves are each co ntrolled by a normalized fracture stiffness. For low values of the nor malized fracture stiffness, the symmetric and antisymmetric interface waves degenerate to the classic Rayleigh wave on a traction-free surfa ce. For large values of the normalized fracture stiffness, the antisym metric and symmetric interface waves become a body S wave and a body P wave, respectively, which propagate parallel to the fracture. For int ermediate values of the normalized fracture stiffness, both interface waves are dispersive. Numerical modeling performed using a boundary el ement method demonstrates that a line source generates a P-type interf ace wave, in addition to the two Rayleigh-type interface waves. magnit ude of the normalized fracture stiffness is observed to control the ve locities of the interface waves and the partitioning of seismic energy among the various waves near the fracture.