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Continued dyking in the Dabbuhu Rift segment, Afar, Ethiopia, from radar interferometry

Ian Hamling(1), Derek Keir(1), Atalay Ayele(2), Eric Calais(3), Cynthia Ebinger(4), Elias Lewi(2), Gezahegn Yirgu(2) and Tim Wright(1)

(1) Institute of Geophysics and Tectonics, University of Leeds, Leeds, LS2 9JT, United Kingdom
(2) Geophysical Observatory, Addis Ababa University, Addis Ababa, Ethiopia
(3) Purdue University, West Lafayette, IN 47907-1397, United States
(4) University of Rochester, 227 Hutchison Hall, Rochester, NY 14627, United States


The 60-km-long Dabbahu segment of the Nubia-Arabia plate boundary lies in the Northern Ethiopian region of Afar. In September 2005 a major rifting episode resulted in the injection of a 60-km-long dyke with a maximum thickness of ~ 8m (Wright et al., 2006). Subsidence observed at Dabbahu and Gabho volcanoes implied that some of the magma was sourced from shallow reservoirs beneath the volcanoes. Using a combination of satellite interferometry, GPS and seismicity we aim to monitor the ongoing deformation in the Dabbahu rift segment. Interferograms in the following months show only isolated deformation around the volcanoes and around the centre of the Dabbahu rift segment. However, in June 2006, intense deformation is observed along a rift parallel, 10 km long zone extending north of Ado’Ale, which is a volcanic complex located in the middle of the rift segment. Modelling of radar interferometry (InSAR) data indicates the injection of a ~2 m thick, ~10 km long dyke, with deformation spatially coincident with seismicity (Keir et al., this session). Since June 2006 a further 5 dyke intrusions have been detected using InSAR – in July, September and December of 2006 and in January and August of 2007. Elastic modelling of InSAR data suggests that a ~2 m thick, ~9 km long dyke was intruded in July 2006 followed by a ~2 m thick, ~8 km long dyke in September, neither dyke reached the surface and both dykes were confined to the upper 10 -12 km of the crust. Preliminary results suggest similar styles of intrusion for the December 2006 and January 2007 dykes. A fissural basaltic eruption occurred with the August 2007 deformation showing that the dyke reached the surface. . All dykes since June 2006 are south of the Ado Ale complex – a rifted silicic centre in the middle of the rift segment. InSAR and GPS show no deflation at either of the volcanoes at the northern end of the segment implying an alternate source is feeding the ongoing intrusions. We do not observe surface subsidence associated with any source region, and thus require a deep source (~ 8 km) and suggest that this is located near the centre of the rift segment. The apparent migration sequences seen so far appear to be similar to those seen in Iceland during the 1975-1984 Krafla rifting episode, and we anticipate further dyking episodes and eruptions over the next few years.


Keywords: ESA European Space Agency - Agence spatiale europeenne, observation de la terre, earth observation, satellite remote sensing, teledetection, geophysique, altimetrie, radar, chimique atmospherique, geophysics, altimetry, radar, atmospheric chemistry