Australian crustal structure

There have been eight large-scale refraction experiments in Australia during the last fifteen years. P₁ velocities derived from these experiments are significantly higher in the Precambrian shield region than in eastern Australia. P_n-velocities are also higher beneath the shield, and appear to increase systematically from east to west across the continent. There is good evidence for an intermediate layer in all parts of Australia, with an average depth of about 20 km to the Conrad discontinuity. The crustal thickness has an average value of about 40 km, and the observed variations in thickness are apparently unrelated to topography in most cases.