Earth models based on compressibility theory

Abstract

An Earth model, Model B, constructed some years ago on the basis of a ‘k-p postulate’ (k = incompressibility, p = pressure) , has now become obsolete. The causes arise, not from any recent change of attitude on the k- p postulate, but from a revision of the estimated moment of inertia of the Earth, revisions of the seismic P velocity distribution in the core, evidence on the Earth's central density (ρ 7) and evidence from free Earth oscillations. The present paper is concerned with replacing Model B by new models in which the k- p postulate continues to be adopted but the new evidence is taken into account. In part, the paper is an extension of calculations recently carried out for the lower core (the regions E″, F, G below). In replacement of Model B, two base models, B 1 and B 2, and several closely related models are derived. The models give sets of values of p, k, the density ρ, rigidity μ, gravitational intensity g, and several other variables, in terms of the depth below the surface. With the models of B 1 type, it is assumed that the seismic S velocity, where not zero, follows in the core a similar pattern of variation to the P velocity; for these models, ρ 7 ≈ 15 g/cm 3. With the B 2 type, the S velocity distribution in the lower core is selected so as to yield the minimum value of ρ 7 compatible with the k- p postulate; for these models, ρ 7 ≈ 13 g/cm 3. Models which differ from the base models exhibit the effects of changing various parameters such as the core radius, the density gradient in the upper mantle, etc.