Analysing fault growth at the continental break up zone in Afar, Ethiopia

Many studies on fault scaling relationships have been undertaken in amagmatic regions, and/or in settings where faults are relatively mature. However, recent acquisition of high-resolution LiDAR data from the Manda-Hararo Rift, Afar, has enabled us to derive a DEM of 0.5m spatial resolution, which in tandem with field observations and InSAR data, provides a unique opportunity to quantify the earliest stage of fault evolution in a magmatic rift. In September 2005, a rifting episode commenced in this region and about 2-2.5 km3 of magma was injected into a 60-km-long dyke. Horizontal opening of up to 8m occurred, inducing normal slips of up to 3m on faults that crop out at the surface. Since then, 13 further dyke intrusions showing surface deformation have been detected and analysed using InSAR data. For comparison with previous fault growth studies, we have undertaken a morphometric analysis of cumulative fault displacement within the narrow axial zone. With the exception of Dabbahu Volcano and the dissected remnants of the Ado’Ale Central Volcanic Complex, much of this region is set in Pliocene flood basalts with little natural surface relief, thus forming an ideal study area for quantifying cumulative fault growth. Young faults manifest in the geomorphology as steep scarps, monoclines and associated fissures. These structures are densely distributed, and dissect the axial zone into polygonal fault-blocks with sub-horizontal top surfaces. Both monoclines and faults sensu stricto contribute to the vertical displacement across fault blocks, but detection of the lateral tip of the former is difficult. We therefore apply an automated method to systematically derive the distribution of vertical displacement between adjacent fault blocks and use this data set as a proxy for fault displacement. Here we present first results of our statistical analyses of these data.