Re-orientation of the extension direction and pure extensional faulting at oblique rift margins: comparison between the Main Ethiopian Rift and laboratory experiments

• Published in: Terra nova (Oxford, England) Vol. 25; no. 5; pp. 396 - 404
• Main Authors: Corti, Giacomo, Philippon, Melody, Sani, Federico, Keir, Derek, Kidane, Tesfaye
• Format: Journal Article
• Language: English
• Published: Oxford Blackwell Publishing Ltd 01-10-2013; Wiley-Blackwell
• Subjects: Continental dynamics; Earth Sciences; Earthquakes; Fault lines; Sciences of the Universe; Tectonics; Africa
• ISSN: 0954-4879; 1365-3121
• DOI: 10.1111/ter.12049

In this study, we draw on a unique combination of well‐resolved fault‐slip data and earthquake focal mechanisms to constrain spatial variations in style of faulting in the obliquely extending Main Ethiopian Rift, East Africa. These data show that both boundary and internal faults – oblique and orthogonal to the plate divergence (PD) respectively – exhibit almost pure dip‐slip motion, and indicate significant local deflection in orientation of the extension direction at rift margins. Scaled analogue models closely replicate the multidisciplinary observations from the rift and suggest that the process is controlled by the presence of a deep‐seated, pre‐existing weakness – oblique to the direction of PD – that is able to cause a local rotation in the orientation of the extension direction at rift margins. Minor counterclockwise block rotations are required to accommodate the difference in slip direction along the different fault systems, as supported by existing and new palaeomagnetic data from the rift.