IMPLICATION OF SHEAR DEFORMATION AND EARTHQUAKE DISTRIBUTION IN THE EAST-AFRICAN RIFT BETWEEN 4-DEGREES-N AND 6-DEGREES-N

The distribution of earthquakes since 1900 in the East African Rift System between 4°N and 6°N is discussed. Recent crustal deformation corresponding to shear failure associated with earthquakes and offset in the major rift faults demonstrate that the northern part of the East African Rift System is characterized by a NW-SE trending active shear zone corresponding to an intracontinental transform fault zone. In this zone, stepped strike-slip and normal faults are shown to be jointly active in determining the mechanical process of rifting in the region. The constraint the newly identified zone of transform movement imposes on plate kinemetics of the region is examined. As a result, it is possible to discriminate among poles of relative motion suggested for the African/Somalian plates by numerous workers. © 1990.