Variations in physical properties within the Earth's crustal layers

An investigation of amplitudes of P̅‐waves in southern California in about 300 instances, having epicentral distances from 50 to 570 km, indicates that the velocity V of longitudinal waves in the granitic layer at depths h (in km) between about 2 km and its bottom at about 18 tan is given by V = (5.56 + 0.001 h) in km/sec. The second term is a first approximation only and indicates an increase in the bulk‐modulus by about ¾ per cent corresponding to an increase in pressure by 1000 atmospheres. This is of the same order of magnitude as the values found for granite in laboratory experiments and from the theory of finite strain.