The effects of water-saturated cracks on seismic velocity and anisotropy in crustal rocks


Liu, B.; Wang, B.S.; Xu, D.Y.; Popp, T.; Kern, H.

Acta Geophysica Sinica 42(5): 702-710

1999


P-and S-wave velocities as well as their anisotropy have been measured on four dry and water saturated crustal rocks under different confining pressures. At atmospheric pressure P-wave velocities in the saturated low-porosity (<1%) rocks are markedly higher than that in the dry rocks, as the differences between their S-wave velocities are not significant. Since in low-porosity rocks P-wave velocities are more sensitive to crack fluids than S-wave velocities, the Poisson's ratio can be used to indicate the effect of intercrystalline fluids on seismic properties as confining pressure increased. Basing on the experimental data and the model described by O'Connell et al., we calculated the crack density (Epsilon ) in dry and saturated rocks, that is well correlated to the crack porosity derived from the volumetric strain curve determined experimentally. The S-wave velocity and polarization can be used to determine the spatial orientation of oriented cracks in the rock samples. The simultaneously measured P-and S-wave velocities as well as their ratio Vp/Vs may give evidence for fluids at grain boundaries, and an estimate of crack densities in rock samples.