Comparison of static and dynamic measurements of compressibility of rocks

The elastic properties of several rocks, fused quartz, aluminum, and steel were calculated as a function of pressure to 10 kb from measured velocities of P and S waves in three directions. Compressibility calculated from Vp and Vs is within a few per cent (and therefore within the experimental error) of that measured directly by the use of strain gages, for pressures which range from 3 to 9 kb. Comparison is also good for fused quartz, steel, and aluminum, as well as for fine-grained limestone at atmospheric pressure. At atmospheric pressure a discrepancy of several hundred per cent between static and dynamic values is probably due to the different effects of cracks in the rocks on the two measurements. The good agreement of the two sets of compressibilities at pressures greater than 2 kb implies that other elastic properties calculated from velocities will be in good agreement with static values.