Investigation of interface wave propagation along planar fractures in sedimentary rocks

We have measured ultrasonic Rayleigh and interface waves along laboratory induced planar fractures on Anstrude limestone under dry conditions. Comparing measurements of the Rayleigh wave along rough and smooth surfaces we observe that the effect of the roughness on the surface wave propagation is to induce attenuation and velocity dispersion. The attenuation increases linearly with frequency; the phase velocity goes through a maximum at 240 kHz. We put forward a physical model describing the effect of the roughness in terms of an increase in the effective length of propagation. This model predicts a frequency dependence of an order that scales with the magnitude of the roughness. We have also compared measurements of the interface wave with measurements of the Rayleigh wave, along a single rough surface, to observe the effect of stress on the interface wave propagation. Within the range from 0 to 10 MPa, the interface wave velocity and its amplitude increased with the applied stress.