Compressibility-Pressure Gradient and the Constitution of the Earth's Outer Core

Abstract

Re-interpretation of seismic data used by Birch in respect of the Earth's outer core indicates that his finite-strain theory, while serviceable to a useful first approximation, is probably not adequate for drawing fine conclusions on the variation of the incompressibility with pressure in the core. On currently available seismic data, there is a strong suggestion of mild inhomogeneity inside the outermost 700 km of the core. The whole region from 2700 to 3600 km depth seems to be slightly abnormal, with a faint suggestion of continuous change of phase in the outer part of the core. The conclusions are sensitive to the values in determinations of seismic P velocity gradients in the outer core, and it is desirable that some renewed attention be given to estimating the precision of the determinations.