Alemu Abera (PhD)ZemIchael Lijam2018-06-292023-11-182018-06-292023-11-181997-06http://etd.aau.edu.et/handle/12345678/4929All available data, over 3000 stations, obtained from the EIGS and the Geophysical observatory (Dr. Abera's Ph.D work) were reduced to sea level with a uniform crustal density of 2.67 gmicm3 • Effects of Bouguer masses were calculated applying the simple Bouguer cOITection. Terrain correction was not applied in which case its effect was treated as systematic error in computing the over all mean square elTor of the simple Bouguer anomalies at each station. Theoretical gra\·ity field was computed by means of the intemational gravity fonnula of 1967 (GRS67) and tied to the IGS};71. The accuracy of the Bouguer anomaly at each station is calculated to about ± 2.5 mga!. The regional and residual gravity field were calculated from the Bouguer anomaly map by mea~ of a computer software. The compiled Bouguer anomaly map shows a strong con'elation between the regional pattern and topographic feature of the survey area. Owing to higher elevations, the adjacent plateaus are marked by negative Bou"ouer anomalies. the minimum of magnitude -270 mgals being located around Debreberhan for the study area. The maximu'm gravity values occur in the Afar de]Jression conesponding to the relatively lower elevations. TIle main Ethiopian rift including Afar is characterized by a relatively positive anomaly as compared to the plateaus. The high on the rift accounts for the excess mass at depth on which the crust lies relative to the plateaus where a mass deficiency is assumed. Gravity values on the main Ethiopian rift are generally less than those in the Afar. TIils accounts for the th. inning of crust material towards the .-\far along the rift, or it can equall.y be explained as by a thickening of a denser material beneath the crust (probably the anomalous mantle). The margins separating the rift £i'om the plateaus are marked by steep ~ gra\ity gradients with their magnitude' representing the slope of the escarpment. Steep gradients characterize the transition of gra\.ity fidd from the plateaus to the rift floorenStudies In fuelThesis