The velocity Vp of compressional waves has been measured in rock samples of low porosity to confining pressures Pc of 2 kb for a number of different constant pore pressures Pp. An effective pressure defined by Pe = Pc − nPp, n ≤ 1, is found to be the determining factor in the behavior of Vp rather than an effective pressure defined simply by the differential pressure ΔP = Pc − Pp. As pore pressure increases at constant effective pressure, the value of n increases and approaches 1, but as effective pressure increases at constant pore pressure, the value of n decreases. These observations are consistent with Biot's theory of the propagation of elastic waves in a fluid‐saturated porous solid.

The lunar velocity profile and laboratory data on terrestrial and lunar rocks are constraints on models of lunar history. They show that shock-induced microcracks are absent from the rocks present in the moon today at depths of 25 to 60 kilometers. All possible causes of this observation are examined, and the most likely explanations are that either the rocks at depths of 25 to 60 kilometers formed after the major impacts ceased or the microcracks have annealed at temperatures of about 600 degrees C over geologically long times.

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