The continental layers of Europe‡

Abstract

The observed period and group velocities of Love waves propagated across Eurasia indicate that the thicknesses T₁ and T₂ of the granitic and intermediate layers of Eurasia satisfy the approximate equation 2T₁ + T₂ = 65.5 ± 6 km. If the equation obtained by Jeffreys from Japanese deep-focus earthquakes, T₁ + 0.85 T₂ = 30.3 ± 1.3 km., is accepted, we find T₁ = 36.2 ± 7.4 km., T₂ = −6.8 ± 9.4 km., implying that the thickness of the intermediate layer is not significantly different from zero. Taking T₂ = 0 would then give T₁ = 33 ± 3 km. This value does not seem compatible with the observed rate of outflow of heat; but the data concerning the rate of generation of heat through radioactive disintegration are very uncertain. Combined with the Love-wave equation, the isostatic equation indicates a thickness of about 30 km. for the floor of the Pacific Ocean; this is in general agreement with the work of Byerly and Vening Meinesz. The deep-focus earthquake equation then indicates that the base of the granitic continent, without any “intermediate layer,” should be at about the same level as the lower surface of the basalt layer under the Pacific Ocean, both continent and ocean floor resting on the horizontal surface of ultrabasic material. The need for further investigations into the propagation of surface elastic waves is manifest.