Shear Waves through the Earth's Core

Abstract

IN 1914, Gutenberg¹ published an analysis of earthquake waves arriving at great distances, in which he inferred the existence of a major surface of discontinuity at a depth of about 1,800 miles, bounding a central core within the earth. His predictions regarding the characteristics of eompressional (P) waves transmitted through this core have been abundantly verified. But until recently, no signs have been forthcoming of the existence of distortional (S) waves that had penetrated this central mass. The conclusion has thus gradually come to be accepted that the core is in a fluid or semi-fluid state, and is thus incapable of transmitting shear waves that reach its boundary. Two branches to both types of core waves were indicated by Guten berg's theory, and have been designated by Macelwane P_l and P₂, S₁ and S₂ respectively.