Gravity Field of the Central Portion of the Main Ethiopian Rift

Recently, we have acquired new gravity data along the axis of the central portion of the Main Ethiopian rift. The survey was designed to have close station spacing, and high precision GPS measurements where made to insure positioning was precise. We combined our new data with previous data available for the region to produce an improved map of the gravity anomalies in the region. Our analysis shows that this portion of the Main Ethiopian rift is characterized by a broad gravity high that follows the physiographic riftt valley with localized short wavelength gravity highs in several places within the rift valley. These anomalies correlate with known volcanic centers such as the Aluto volcano (Geothermal field), the Gadamota caldera, Bora volcano, Corbetti caldera and Lake Shalla areas. Further to the northeast, the Gedemsa caldera and the spreading center known as the Wonji fault belt (WFB) are depicted as a gravity high trending northeast towards Afar. We have derived an axial gravity model that is constrained with seismic data from the EAGLE project and models for NW - SE profiles that cross the rift perpendicularly. Some filtering techniques have been applied to provide gravity anomalies of local and deep crustal origins. The eastern and western plateaus are characterized by relative gravity minima. However we have found that the eastern plateau has a more negative anomaly than the western plateau, and the difference is about 20 mGal. This may indicate that the eastern plateau has a thicker crust than the western plateau.