Asfaw, Laike Mariam (PhD)Alemu, Abera2018-06-122023-11-092018-06-122023-11-091983-06http://10.90.10.223:4000/handle/123456789/493A detailed gravity survey of the Main Ethiopian Rift Valley between latitudes 70 N and SON, has shown that there is a broad relative positive Bouguer anomaly over the whole of the Rift floor, and this anomaly is superimposed on the regional, broad negative anomaly of the Ethiopian and Somali Plateau. The broad relative positive anomaly over the rift floor is between 60 and 100 km wide and has an amplitude of 30 - 60 mga!. On the broad relative positive anomaly over the rift floor are superimposed other short-wave length relative positive anomalies which seem to be situated along the displacement lines of the Wonji Fault Belt. There are also much narrower relative positive anomalies along the margins of the rift other than those associated with the \'Ionji Fault Belt. In their interpretation of the gravity minimum near the center of profile C (page 47), Searle and Gouin (1972) suggested that this gravity minimum is due to low density lavas of the Aluto volcano and they further a.8sociated the volcano with a small negative anomaly. On the contrary the present survey shows that the volcano is associated with a relative positive anomaly of magnitude comparable to the short-wave length rela.tive positive anomalies along the displacement lines of the Vionji Fault Belt. Due to both, denser spacings of gravity stations and quality of data, it is believed that the present gravity survey of the Main Ethiopian Rift between latitudes 70N and SON defines more accurately the location of the gravity anomalies (both the negative and the positive anomalies). The priliminary interpretations of the gravity anomalies made in this work are corroborated by bore hole data Wigs. 10, 11 ) and surface geology (F.ig. 2) of the study area. Furthermore, inferred density measurements on surface rocks and Cores from production bores in the Olkaria geothermal field of Kenya (Table 2) have been utilizedenEthiopian Rift ValleyThesis