Preface

Abstract

This chapter discusses that East African rift system (EARS), which displays dramatic subfacial, crustal, and upper mantle contrasts, some of which have been delineated in detail by geological and geophysical studies. Crustal models derived from recent seismic studies in the Kenya rift show no evidence for major intrusions and densification of the crust beneath the rift as it inferred primarily on the basis of gravity models. The Kenya rift also displays striking east west symmetry. The presence of zones of very low seismic velocity in the upper mantle directly beneath rifts and associated crustal thinning suggest that active mantle processes are the primary cause of rifting in Kenya and Ethiopia. The EARS provides classic examples of continental rifts in Ethiopia, Kenya, and the Western rift. There are strong similarities between these rifts and other continental rifts such as the Rio Grande rift and the Baikal rift. Rifts, which have relatively narrow geologic features in their surface expression, may be underlain by a relatively narrow, hot, and upper mantle upwarp.