Processing and interpretation of full tensor gravity anomalies of Southern Main Ethiopian Rift

Abstract

The study area is situated in the Southern Main Ethiopian Rift being bounded within the limit of 37o00″0′-38o50′00″E and 5o50′00″-7o00′00″N. It is well known that the complex geological structure of the Main Ethiopian Rift has attracted intense attention so far and numerous geophysical investigations have been performed using potential field data-sets in Central and Northern Main Ethiopian Rift with the exception of the Southern Main Ethiopian Rift which is poorly constrained. Analysis of Full Tensor Gravity anomalies helps in understanding of the nature of shallow subsurface structural features and has a paramount importance in building general understanding of subtle details about subsurface geology of the area. Separation of regional and residual gravity field is performed using upward continuation filtering technique. The residual gravity anomaly caused by local structures and anomalous body delineated four sub-basins with low amplitude response which is in agreement with the vertical gravity gradient anomaly (Gzz) and tilt derivative horizontal (TDX) that clearly outlined and characterize edges of the sub-basins. The sub-basins delineated are the northern and southern Abaya, Chamo and Gelana basins. The tilt angle method which is used to delineate major subsurface structures and determine the source depth results showed that the area was affected by different lineament trending NE-SW, N–S, NNE-SSW, NW-SE and E-W, directional analysis performed indicates that the dominant trend is in agreement with the regional fault orientations. The estimated depth to the top of the lineaments on average varies from 0.9 km to 3.1 km and it is relatively deeper in the basins compared to the surrounding areas giving clues to the amount of sediment infill.