An aeromagnetic survey of the afar triangle of Ethiopia

Abstract

In 1968, an aeromagnetic survey was flown over the Afar triangle of Ethiopia. The survey extended from 9.5° N to 15° N and was bounded in the west by the Ethiopian scarp (about 40°h E) and in the east extended over the Gulf of Tadjoura and the western part of the southern Red Sea. The flight height was 1.83 km (6000 ft). 34 profiles were flown in a direction N 100° and 42 profiles in a direction N 150°, the spacing between profiles being about 10 km. In addition, there were 14 tie lines. The total flight path was approximately 24000 km. The magnetic and radioaltimeter records were digitised and profiles prepared showing both total intensity magnetic field (with I.G.R.F. epoch 1965.0 removed) and topography. Several analyses have been carried out: correlation studies were made in an effort to find trends and locate transform faults. Spectral analyses have yielded information on the shape, size and depth of the causative bodies and correlations between the magnetic anomalies and the geology are being studied. In addition, a coloured magnetic anomaly contour map has been prepared with contour interval 100 nT, and scale 1:1,000,000 at 33° N. The contour map reveals several interesting features. First, the magnetic lineations previously mapped in the Gulf of Aden are found to extend westwards over parts of southern Afar. Secondly, there are regions of small amplitude, short wavelength anomalies which are thought to be associated with continental (sialic) material. Thirdly, the anomalies north of about 12° N have a NW-SE trend fanning towards the south. The bearing of the survey on the tectonic evolution of the area is discussed. A full account is in preparation with large format diagrams.