Correction of gravity anomalies at sea for submarine topography

Abstract

It is suggested that the correction of sea gravity data for submarine topography be computed for a datum surface coinciding with the surface of a standard oceanic crust and with the surface of a standard continental margin. The standard continental margin is a transitional zone between the standard continental and oceanic crusts. Every column of it, including the upper part of the mantle down to the isopiestic level, is in isostatic equilibrium with similar columns of the standard continental and oceanic crusts. Two models of the standard continental margin are given. Sea gravity anomalies reduced in the manner given in the paper are called ‘modified free-air anomalies.’ They are free of the gravity effect of submarine topography; consequently they represent the gravity effects of the deviations of the actual crust from the standard crust. Over continental margins a correction for the edge effect of the continent must be applied. A unified world-wide isogal map over continents, oceans, and continental margins can be constructed by using Bouguer anomalies on land and modified free-air anomalies over the sea if both types of anomalies are corrected for the edge effects of the continents. The modified free-air anomalies are directly related to the deviations of the actual crust from the standard crust; thus the interpretation of sea gravity data is simplified. The interpretation of modified free-air anomalies along a profile is illustrated by an example.