Evidence for an Intermediate Layer from Crustal Structure Studies in the Eastern Transvaal.

Abstract

Summary Observations of the travel times of waves from Witwatersrand earth tremors along a route in the Eastern Transvaal are reported in this paper. It is considered that the most satisfactory interpretation is that the crust is two-layered. The velocities in the granitic layer are 6·0 and 3·6 km/s for P and S waves respectively. In the intermediate layer the P velocity lies between 6·7 and 7·2 km/s, and the S velocity between 3·95 and 4·15 km/s. The Pn velocity was found to be 7·96 km/s and the crustal thickness 36·6 km. It was found that Pn arrivals at stations close to sea level were early with respect to the travel-time found for the plateau at a height of about r 750 m.