Dispersive Waves Propagating along a Surface Fracture

Significant work in the past few decades has lead to a well developed understanding of seismic wave propagation in fractured media. However, previous research has focused on fractures within rock as opposed to fractures at the surface of a rock. A theoretical and experimental study was performed to examine seismic wave propagation along a fracture at the surface, i.e., along the intersection of two quarter-spaces. A theoretical model that couples two wedges, using displacement discontinuity boundary conditions, was developed that gives rise to a new guided waveform that is dispersive, depends on fracture specific sti↵ness at the intersection of a fracture with a free surface and exhibits velocities that range from the single wedge-mode velocity to the Rayleigh wave velocity at a free surface. The existence and behavior of this new guided-mode was verified using a synthetic fracture created between two aluminum blocks. This new guided-mode enables characterization of fracture specific sti↵ness of fractures, joints and other discontinuities at the surface of an outcrop.