Some Recent Geophysical Studies of the Rift System in East Africa

Abstract

Seismicity maps are used to demarcate the African plate and regions where the plate maybe breaking into smaller plates. One of these is the Gregory rift through East Africa. In this region, complete crustal separation has not taken place as in the Red Sea and Gulf of Aden. Instead, extension seems to have caused attenuation of the lithosphere with accompanying rifting and volcanism. The ages of rift faults and volcanoes tend to increase with distance from the axis of the rift. Three sets of geophysical data can be used to support plate attenuation. These are (i) the long wavelength negative Bouguer anomaly which is found over a large region of East Africa; (ii) the attenuation of Sn for paths crossing the rift north of 10°S. and (iii) microseismicity studies of the rift floor. The long wavelength negative Bouguer anomaly has been interpreted as being due to the low-Q asthenosphere engulfing the lower part of the lithospheric plate. It is suggested that the areal extent of the regional negative Bouguer anomaly might be used to map the region of plate attenuation.