The great negative Bouguer gravity anomaly over Africa


  • Ronald W. Girdler


This article draws attention to a most remarkable feature on a recently published Bouguer gravity anomaly map of Africa. The map is published by the U.S. Defense Mapping Agency in a technical paper that may not be widely seen, although it was presented at the Spring Annual Meeting of the AGU in 1973. The authors are R.L. Slettene, L.E. Wilcox, R.S. Blouse, and J.R. Sanders [Slettene et al., 1973].

The map is on a Mercator projection at a scale of 1:20,000,000. The compilation procedure was completely automated, and only terrestrial data were used. A total of 3073 mean anomaly predictions 1°×1° were incorporated. About 40% of these were computed by various conventional and statistical methods; the remaining 60% were made by geophysical correlation methods. The computer-generated contours are at 10 mgal intervals for anomalies smaller than −100 mgal and at 20 mgal intervals for anomalies larger than −100 mgal.