The Velocity of Sound in Rocks and Glasses as a Function of Temperature

Measurements show that the velocity of sound in Pyrex and in silica glass rises with increasing temperature and that these substances support vibrations substantially without loss to temperatures above 700º C. Measurements on rock samples show a decrease in velocity with increasing temperature, only part of which is reversible as the material cools. This permanent reduction in velocity is explained by differential thermal expansion. The reversible temperature effect on velocity of sound is less than 1 per cent per hundred degrees in granite, and about 5 per cent per hundred degrees in diabase. The geophysical significance of these results is discussed.