Abstract:
Over the past ~30 Myr rifting of Africa and Arabia has resulted in the ~300 km wide Afar Depression. The Red Sea arm of the Afar triple junction encompasses the subaerially exposed ~60 km long volcanically and tectonically active Dabbahu Manda-Hararo (DMH) magmatic segment, which is one of the few places where incipient seafloor spreading is observable on land. Recent activity commenced September 2005 resulting in dykes, faults and earthquakes. To better study this region, detailed structural maps have been constructed using three different resolution remote imagery datasets. These consist of high-resolution Light Detection and Ranging (LiDAR) data at 0.5 m resolution, Satellite Pour l'Observation de la Terre (SPOT) data at 6 m resolution, and Shuttle Radar Topography Mission (SRTM) data at 90 m resolution. A consistent method for manually picking faults was developed for each dataset utilizing several topographic attribute surfaces (slope, aspect, aspectslope, curvature, and hillshade) as well as using quantitative criteria based on the accuracy and limitations of the data (vertical and horizontal errors). Normal faults and fissures in this region strike NW-SE, oblique to the direction of extension. To the north of the segment near the Dabbahu Volcano faults trend NNW-SSE. It has been determined that swing in the rift axis is the determining factor in this change in fault orientation rather than tectonic loading. Nodes for each structure were then defined depending on fault interactions, such as “i” for ends, “x” for crossing, and “y” for branching. The distributions of these nodal networks have been analysed to observe the nature of rifting in this region via the interpretation of lineaments. It was shown that deep seated WNW-ESE trending preexisting structures were found to act as initiators and barriers to the propagating of dykes; utilizing seismic swarms as a proxy.
