New evidence for Afro-Arabian plate separation in southern Afar
Published:January 01, 2006
Atalay Ayele, Andrew A. Nyblade, Charles A. Langston, Michel Cara, Jean-J. Leveque, 2006. "New evidence for Afro-Arabian plate separation in southern Afar", The Afar Volcanic Province within the East African Rift System, G. Yirgu, C. J. Ebinger, P. K. H. Maguire
Download citation file:
The May 2000 earthquake cluster, around 10° N and 41° E in southern Afar, has been studied using high quality data from 12 temporary and permanent broadband seismic stations deployed in the area. 140 earthquakes have been located using P- and S-wave arrival times, a well-constrained velocity model, and a double-difference location algorithm. Source mechanisms and moment magnitudes for the four largest events (M > 4) have been obtained from moment tensor inversion. There is no clear alignment of the epicentres along a fault zone; however, the events are clustered slightly southeast of Mount Amoissa along WNW—ESE extension of the Ayelu—Amoissa (Abida/Dabita) lineament. Focal mechanisms show fault motion along WNW—ESE to east—west striking normal faults, with extension oblique to the orientation of the Main Ethiopian Rift. The non-double-couple components of the source mechanisms range from 18–25%, suggesting that the seismic activity is of tectonic origin and not volcanic. Source depths are ≤7 km, in good agreement with estimates of the elastic thickness of the Afar lithosphere. We suggest that the Gewane earthquake swarm represents remnant strain accommodation along a previous line of weakness in southern Afar related to the separation of Arabia from Africa because the focal mechanisms show north—south extension similar to many of the events in central Afar at the triple junction where Arabia is presently rifting away from Africa.
Figures & Tables
The Afar Volcanic Province within the East African Rift System
The seismically and volcanically active East African Rift System is an ideal laboratory for continental break-up processes: it encompasses all stages of rift development. Its northernmost sectors within the Afar volcanic province include failed rifts, nascent seafloor spreading, and youthful passive continental margins associated with one or more mantle plumes. A number of models have been proposed to explain the success and failure of continental rift zones, but there remains no consensus on how strain localizes to achieve rupture of 125–250 km thick plates, or on the interaction between the plates and asthenospheric processes. This collection of papers provides new structural, stratigraphic, geochemical and geophysical data and numerical models needed to resolve fundamental questions concerning continental break-up and mantle plume processes. It focuses on how mantle melt intrudes and is distributed through the plate, and how this magma intrusion process controls along-axis segmentation and facilitates break-up.