This study will examine the structure and late Cenozoic tectonism in the Afar region (East Africa) in an effort to decipher the neotectonic framework of an active rift-rift-rift triple junction. The interaction between the Gulf of Aden and Red Sea rifts may have led to the development of a large scale accommodation zone that presently is marked by half grabens and tilted fault blocks in central Afar. Understanding the partitioning of extension across Afar rift will provide insight into the evolution of rift-rift-rift triple junctions and continental rifting, in general. Comparison of long-term (Quaternary) deformation with more recent kinematics (e.g., from late Pleistocene landforms and available GPS observations) provides an initial means of assessing the evolution of the accommodation zone (e.g., co-axial strain versus progressive strain and rotation). The structure and tectonics of central Afar will be investigated from remote sensing data and field studies to better understand the linkage between the Red Sea and Gulf of Aden rift propagators into central Afar. In particular, the research will focus on the Afar Stratoid volcanic rocks (approximately 4.0 to 1.0 Ma), a regionally extensive lava surface that predates the initiation of grabens in central Afar. ALOS PRISM & PALSAR data will be utilized to generate high resolution digital topographic base maps, and ASTER & AVNIR-2 images will be used to discriminate geomorphic and lithologic features. Field observations will provide ground-truth verification for the remote-sensing-based regional mapping. Investigations will involve local mapping of the geological structure, Quaternary geology, and geomorphology. This activity will constrain the geometry of fault-related landforms and other landscape elements that could provide markers of recent tectonic activity. Field investigations will also document and measure basic structural data. Combining structural and neotectonic analyses, we aim to accomplish the following: 1) determine the presence of an accommodation zone between the propagating Red sea and Gulf of Aden rifts; 2) constrain structural geometries and the viability of a regional datum for restoration; 3) document the contribution of small faults to regional strain; 4) estimate horizontal extension across part of the central Afar; and 5) assess late Pleistocene tectonic landforms as kinematic indicators and potential for estimating rates.
The Afar region encompasses the only sub-aerial exposure of a rift-rift-rift triple junction and, hence, affords a unusual opportunity to study the extensional tectonism from the early break-up of continents to seafloor spreading. Present-day extension across the Afar is accommodated by magmatic, axial rift zones (the Red Sea and Gulf of Aden propagators and the main Ethiopian Rift), and amagmatic extension across the intervening region in between. As an exploratory project this work will facilitate the development of new international collaborations between US universities and colleagues in Ethiopia and Djibouti. As with neotectonics studies, in general, results will contribute to a more informed assessment of the earthquake hazard in the region, although implementing that link is beyond the scope of this pilot study. Although the Afar region is sparsely populated urban and infrastructure development including dam and irrigation schemes, large scale commercial farms, roads, and railway lines have taken place. Past earthquakes including the Serdo (1969) and Dobe (1989) in central Afar have disrupted road networks that provide Ethiopia access to the sea.
This project is supported by the Earth Sciences Division Tectonics Program and the NSF Office of International Science and Engineering.
The Afar region encompasses the only sub-aerial exposure of a rift-rift-rift triple junction and, hence, affords a unique opportunity to study the extensional tectonism from the early break-up of continents to seafloor spreading. This pilot project, a collaboration between the University of Missouri and Lincoln University, initiated field-based studies of recent faulting in the central Afar region, primarily in Ethiopia, but also in neighboring Djibouti. Goals included assessing the appropriateness of specific methods and establishing collaborative ties with local institutions that could support a larger research effort. A 3-week field investigation was conducted during the 2012-2013 winter, and lab-based methods of inquiry included analysis of high-resolution satellite imagery and structural modeling of field and other observations. Intellectual Merit: Whereas prior research in the Afar has primarily focused on the magmatic rift basins, this project began to exam faults in the region undergoing extension in the absence of volcanic activity. In particular, significant effort focused on the amagmatic Dobe Graben in Ethiopia. Key results pertain to fault interactions and total fault-related deformation. (1) Based on analysis of faulted landforms, the study proposed initial estimates of rates of faulting in the basin. Compared with faulting rates and adjacent basin, it appears that extension rates in the Dobe Graben rates differ by 30 – 40%. This suggests that some other deformation mechanism must accommodate some missing strain as a link between the two fault systems. (2) Structural modeling of the Dobe Graben suggests that the long-term (~1 million year time scale) average rate of crustal stretching is similar to that estimated from younger landforms (10,000 – 20,000 time scale). This suggests that rates of tectonic activity have been approximately constant since the current episode of rifting began. (3) The study also began to examine the contributions to total deformation of faults of different sizes. This was accomplished by mapping and measurement of faults using high-resolution satellite imagery (2.5 meter pixel) and digital elevation models derived from that imagery. Initial results suggest possible spatial variations in the statistical relationship between fault length and displacement. Broader Impacts: In addition to the scientific results, this project provided research experiences (including field work) for two undergraduate students from the University of Missouri (as well as an undergraduate student from Lincoln University). The project also initiated the dissertation research for a Ph.D. student. As an exploratory project this work facilitated the development of new international collaborations between US universities and colleagues in Ethiopia and Djibouti. As with neotectonics studies, in general, results will contribute to a more informed assessment of the earthquake hazard in the region. Although the Afar region is sparsely populated urban and infrastructure development including dam and irrigation schemes, large scale commercial farms, roads, and railway lines have occurred in the recent past.
