The Gravity Field Southern Ethiopian Rift Systems Between 3.30 to 7.150 Nlatitude and 360 to 420 Elongitude
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Date
1997-05
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Addis Ababa Universty
Abstract
1800 gravity data covering the research area are redilrc t·) f<o'lgu~r tnd !ree ;:ir vdu~s ,an:! interpreted
based on the Bouguer anomaly map and a pair, of sho& w~v" 1~li?,t;i(&\vrJ, re"i(,lualj ' lltld long \yave
length (LWL, regional) anomaly maps. All dat~ are reduced: ;~ ~~a !e;'e! '\~h 'u~i~~~m' ~er.sity of 2.67
g/cm3
• Effect of Bouguer masses were calculated applying the simple Bouguer corrections. Terrain
correction was not applied.
The Bouguer anomly map of the rift zone between 3.30 N to 7.150 Nand 360 E to 420 E is presented.
The geologic and tectonic setting of the area is discussed based on the compilation of gravity data and
synthesis of published 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 reside on its shoulders. Gravity anomaly of magnitude -135
mGal is observed over the Chew Bahir rift 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 simply related 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 leugth components of the Bouguer gravity anomaly the residual gravity
anomaly is interpreted. The residual gravity field exhibits rapid changes of gravity gradients over short
dist.~nce appears to show the presence of faults which bound major rift basins. Anomalous areas are
corelated to their respective geologic interpretation.
The regional gravity anomaly map produced by trending analysis shows the deep stmctural features of
the study area. It shows the transition from negative to positive gravity field 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).
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Keywords
3.30 to 7.150 Nlatitude and 360 to 420 Elongitude