The elastic properties of layered rocks are often measured using the pulse through-transmission technique on sets of cylindrical cores cut at angles of 0, 90, and 45 degrees to the layering normal (e.g., Vernik and Nur, 1992; Lo et al., 1986; Jones and Wang, 1981). In this method transducers are attached to the flat ends of the three cores, the first-break traveltimes of P, SV, and SH-waves down the axes are measured, and a set of transversely isotropic elastic constants are fit to the results. The usual assumption is that frequency dispersion, boundary reflections, and near-field effects can all be safely ignored, and that the traveltimes measure either vertical anisotropic group velocity (if the transducers are very small compared to their separation) or phase velocity (if the transducers are relatively wide compared to their separation) (Auld, 1973).

To discover whether typical experiments of this kind are more likely to measure group velocity, phase velocity, or something in between, we numerically model a laboratory pulse-transmission experiment of Vernik and Nur (1992). In their experiment the separation between source and receiver was more than three times greater than the transducer width. Although this configuration might seem closer to the group-velocity case than the phase-velocity one, Vernik and Nur assumed their recorded first-breaks represented phase velocities.

Our numerical results show Vernik and Nur were (almost) correct. Except for a slight underestimate in the P-wave velocity measurements at 45 degrees to the layering, they did record phase-velocity traveltimes in their experiment. Most experiments are clearly closer to the phase-velocity case than Vernik and Nur's; we therefore conclude that almost all pulse-transmission experiments of this kind should measure anisotropic phase, not group, velocities.