Sequence of rifting in Afar, Manda-Hararo rift, Ethiopia, 2005–2009: Time-space evolution and interactions between dikes from interferometric synthetic aperture radar and static stress change modeling



[1] Thirteen dike intrusions in the Manda Hararo rift, Afar (Ethiopia), from September 2005 to June 2009, studied using an extensive interferometric synthetic aperture radar (InSAR) data set, provide insight into the mechanics of a major active rift. Kinematic inversions of InSAR data reveal that dikes opened by 0.8–3.5 m at an average 5 km depth, with volumes of 0.04–0.2 km3 (with up to 12 m opening and a volume greater than 1 km3 for the September 2005 megadike). Dikes have their source in a midsegment magma reservoir, which induces a local shallowing of the brittle-ductile boundary, presumably due to thermal weakening of the lithosphere. The smaller dikes in 2006–2009 were emplaced in regions of minimum opening of the September 2005 megadike, above the central magma reservoir. In contrast, the most voluminous dike intrusions in 2006–2009 occurred near the locus of the peak of maximum opening of the September 2005 megadike, ∼10 km north of the magma source. This may suggest that tension on the plate boundary was highest there, both prior to 2005 and possibly also after 2005. Evolution and distribution of normal stress on the plate boundary throughout the rifting episode may indicate that tension near to the magma reservoir is lower than toward segment ends. Average relief of normal stresses of tectonic origin coeval to dike intrusions is comparable with shear stress drops for earthquakes, presumably because dikes in the Manda Hararo rift are intruded at low magma pressure and high tectonic stress.