Browsing by Author "Asrat, Estianos"

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    The Gravity Field of the Southern Ethiopian Rift Systems Between 3.30 To 7.150 Latitude and 360 To 420 Longitude
    (Addis Ababa University, 1997-05) Asrat, Estianos; Alemu, Abera (PhD)
    1800 gravity data covering the research a rca are reduce to Bouguer and free air values and interpreted based on the Bouguer anomaly map and a pair of short wave length (SWL, residual) and long wave length (LWL, regional) anomaly maps. All data are reduced to sea level wth uniform density of 2.67 glcm'- Effect of Bouguer masses were calcu lated applying the simple Bouguer corrections. Terrain correction "vas not applied. The Bouguer anomly map of the rift zone between 3.3° N to 7.15° Nand 36° E to 42° E is presented. The geologic and tectonic setting of the area is di scussed based on the compilation of gravity data and synthesis of publi shed papers. A positive Bouguer gravity anomaly of - 165 mGal occur over the rift floor of the Abaya - Chamo rift and is flanked by negative anomalies that res ide on its shoulders. Gravity anomaly of magnitude -135 mGal is observed over the Chew Bahir ri ft floor and flanked by relative positive anomalies on its shoulders, which is different from the MER. This could be due to lacustrine deposits of the rift floor. The free - air anomaly map is si mply relatcd to topographic relief. The uplifted blocks and horsts are characterised by high free - air gravity anomaly and depressions defined by free - air minimum (-40 to - 75 mGal ). The transition from grabens to horsts is marked by sharp free - air gravity gradients (0 to +40 mGal). After removal of the long wave length components of the Bouguer gravity anomaly the residual gravity anomaly is interpreted. The residual gravity field exhibits rapid changes of gravity gradients over short distance appears to show the presence of fa ults which bound major rift basins. Anomalous areas are corelated to their respective geologic in te rpretation. The regional gravity anomaly map produced by trending analysis shows the deep structural features of the study area. It shows the transition from negative to positive gravity fie ld from MER to SER and negative towards the Kenyan rift indicating the distinction between the SER and the other two rift systems (MER and Kenyan rifts).