The Effect of Pressure on the Rigidity of Rocks. I

A dynamical method has been adapted to the measurement of the velocity of torsional waves in cylinders of rock exposed to pressures as high as 4,000 kg/cm², at 30∘ C. and at 100° C. From these results the rigidities of the rocks under these conditions are derived, as well as approximate values for the pressure and temperature coefficients of velocity and rigidity. Very large changes of rigidity are observed in many cases upon the application of the first few hundred atmospheres; at high pressure the change of rigidity with pressure becomes nearly linear and small. The following questions are discussed: stress conditions in aggregates of crystals, the effect of anisotropy upon velocity, the calculation of other elastic parameters from rigidity and compressibility, damping and dispersion in rocks, the effect of combined pressure and temperature on velocity in the earth's crust, and the identification of materials in the crust by comparison with seismological data.