GRAVITY ANALYSIS OF THE CRUSTAL STRUCTURE OF THE MAIN ETHIOPIAN RIFT

The Ethiopian rift is a major tectonic element of the East African Rift system, which is an incipient divergent plate boundary. We used a newly enhanced gravity database and seismic information to produce an integrated interpretation of the crustal structure beneath the Ethiopian rift and adjacent plateaus.A large area was analyzed in order to assess the regional structure within the area that includes the Kenyan and Ethiopian rifts. Broad negative gravity anomalies are present over the Ethiopian Plateau and the Kenyan dome. Residual gravity anomalies, which parallel the major border faults, clearly highlights the segregation between the plateaus and the rift valleys. The application of filtering techniques clearly reveals individual volcanic centers within the rift valleys. Positive gravity anomalies outside the rift valleys may be associated with older structures, that are related to the initiation and propagation of rifting. Along axial profile from the central part of Kenya to the Afar triple junction has been modeled to investigate along-axis crustal variation of the East African rift system, with emphasis on the Ethiopian rift. Gravity modeling was constrained using seismic refraction data from the Ethiopian Afar Geoscientific Lithospheric Experiment and Kenyan Rift International Seismic Project experiments. We are able to delineate thin crust (~26 km) in the Afar triangle with a gradual thickening (~35 - 40 km) southwards towards the Main Central Ethiopian rift (MER). The crust thickness decreases towards Turkana rift to ~22 km, and increases again towards the Kenyan dome. Our integrated model across the MER revealed the Eastern rift flank has thicker crust than the western flank. The cross profile modeled across the southern part of the Afar triple junction shows a shallow Moho. This may be the result of the rift being initiated by a plume as suggested elsewhere in many studies.