Seismic and related evidence on the structure of the Earth'supper mantle

Abstract

A survey is given of seismological and related evidence on the density, incompressibility and rigidity in the outermost 1,000 Km of the Earth. Earlier evidence, including reference to the writer's Earth models A', A and B, is summarized with special reference to sources of uncertainty. Consideration is given to recent evidence from bodily and surface seismic waves, the recent reduction in the estimated moment of inertia of the Earth, and free Earth spheroidal and torsional oscillation data. Reference is made to current work of Bullen and Haddon which points to density gradients less than normal and to reduced S velocities in the upper mantle as well as to a larger radius for the core.