LAUSR

We experimentally assess the impact of microstructure, pore fluid and frequency on wave velocity, wave dispersion and permeability in a thermally cracked Carrara marble under effective pressures up to 50 MPa. The cracked rock is isotropic and we observe that: (1) P- and S-wave velocities at 500 kHz and the low-strain (< 10-5) mechanical moduli at 0.01 Hz are pressure dependent; (2) permeability decreases asymptotically toward a small value with increasing pressure; (3) wave dispersion between (0.01 Hz-500 MHz) in the water-saturated rock reaches a maximum of ~26% for S-waves and ~9% for P-waves at 1 MPa; (4) wave dispersion virtually vanishes above ~30 MPa. Assuming no interactions between the cracks, effective medium theory is used to model the rock's elastic response and its permeability. P- and S-wave velocity data are jointly inverted to recover the crack density and effective aspect ratio. The permeability data are inverted to recover the cracks' effective radius. These parameters lead to a good agreement between predicted and measured wave velocities, dispersion and permeability up to 50 MPa, and up to a crack density of ~0.5. The evolution of the crack parameters suggests that three deformation regimes exist: (1) contact between cracks' surface asperities up to ~10 MPa; (2) progressive cracks closure between ~10 and 30 MPa, (3) crack closure effectively complete above ~30 MPa. The derived crack parameters differ significantly from those obtained by analysis of 2D electron microscope images of thin sections or 3D X-ray micro-tomographic images of millimeter-size specimens.