Dependence of in-situ compressional-wave velocity on porosity in unsaturated rocks

The relation of in-situ compressional-wave velocities to porosities, determined by seismic refraction for unsaturated near-surface rocks from different areas in Arizona, New Mexico, and California, is grossly similar to relations determined by other investigators for water-saturated rock and unconsolidated sediments. The principal difference is that in the porosity range 0.0-0.2, compressional waves travel somewhat more slowly in unsaturated rocks than in water-saturated rocks, and much more slowly, in the porosity range 0.2-0.8. The function, phi = -0.175 ln (alpha ) + 1.56, where phi is the fractional porosity and alpha is the compressional-wave velocity, was obtained as a least squares fit to the experimental data.Bulk densities are reported for all samples; moisture contents are reported in some instances.