Recent crustal deformation in the Ethiopian rift valley

Abstract

Three geodimeter networks have been established in the Ethiopian rift: at latitude 8 1 2 ° N , in 1969; at latitude 7 1 2 ° N , in 1970; and at latitude 6°N, in 1971. All three networks have been remeasured annually since their inception. Line-length changes, previously analyzed on a semi-quantitative basis, have now been obtained from a least-squares adjustment program. A rather complex but hopefully realistic weighting scheme has been applied, and the overall network adjustment sigmas (dimensionless) are close to unity. With reference to an arbitrarily selected datum for each network, station vectors have been derived, each with its appropriate foot point curve. The results confirm a significant motion of station RABBIT in the Wolenchiti quadrilateral, a region of episodic ground cracking and subsidence. Significant motions of stations in the Adama region ( 8 1 2 ° N ) form a complex pattern, but a component of longitudinal motion along the rift seems to be a common feature. In the Langana network ( 7 1 2 ° N ), motions are perpendicular to the rift faults, at rates of up to 12 mm/yr.