Using pulse methods recently developed, direct measurements of the dilatational and rotational elastic wave velocities in igneous rocks were made. D. C. pulses, impressed on 5 MC X-cut piezoelectric quartz crystals, were used to excite sharp, elastic pulses in rocks. The amplified output of similar detector crystals was studied and photographed using suitable oscilloscopes. Two main arrivals of energy were precisely timed, and from the travel times the dilatational and elastic velocities were computed. Velocities were measured with an accuracy greater than 1 per cent. Regarding rocks as homogeneous, isotropic media, the elastic constants were computed from the velocity data. The sample assembly was placed in a pressure cell, surrounded by an oil bath; thus measurements at high pressures and temperatures could readily be made. Measurements were made in the pressure range 1–1100 kg./cm.2 and the temperature range 30–150°C. Samples of granite, quartz monzonite, diorite, andesite, and norite were investigated.
Materials were studied both while enclosed in impervious copper jackets and while exposed to the fluid pressure medium. The enclosed samples had relatively great increases of velocity with pressure at the low pressures, presumably due to closing of initial pore space; the rate of increase became small and essentially linear at higher confining pressures. Open samples had small, linear rates of increase of velocity over the entire pressure range. Pressure increase was accompanied by increase of wave velocities and elastic constants in all cases. Increase of temperature was accompanied by decrease in velocities and moduli. Changes of Poisson's ratio with pressure and temperature were small and erratic.
The reasonably good agreement of the present work at effective frequencies of 2–6 megacycles with earlier measurements at low frequencies suggests that for rocks the effect of frequency upon velocity is negligible, although the data are, as yet, inconclusive. The present work has established a useful method of obtaining direct measurements of elastic wave velocities in rocks. Extension of the pressure and temperature ranges should provide data valuable for comparison with earthquake seismic results for the earth's crust.