Topography at the core‐mantle boundary

Abstract

Analysis of the Earth's gravity field using ratio of gravity to geoid (g/N) and cumulative degree contribution curve techniques improves resolution of the mass, depth, and dimensions of anomalous mass sources within the planet. The source for four of the ten major geoid anomalies of the Earth has large contributions from harmonic degrees 2 and 3, lie at the core‐mantle boundary, and the greatest has a mass anomaly of 4.2·1022 grams. That boundary has a density contrast (4.4 gm/cm³) which is greater than at any other location, including the contrast at the Earth's surface with space. Thus, relatively small vertical undulations of that boundary produce very large mass anomalies. Topographic relief of less than 3 km at the core‐mantle boundary occurs, and accounts for the existence of the largest geoid anomalies occurring on the Earth.