Research in continental rift systems commonly assumes that lithospheric deformation has a similar scale to and is spatially coincident with the surface expression of rifting. However, ongoing continental extension between Nubia and Somalia appears localized to a narrow rift zone (the Main Ethiopian Rift) only in the thin elastic uppermost crustal lid. At greater depths in both the lower crust and mantle lithosphere, very weak materials appear to accommodate extension by viscous stretching over long length scales at lower strain rates, resulting in highly depth-dependent stretching. This possibility is important because it challenges existing understanding of continental rifting and provides an opportunity to investigate the implications of heterogeneous rheology for continental mechanics. Although the Main Ethiopian Rift has been studied with many, none of the previous efforts have extended far beyond the rift zone to provide a synoptic view of the region. Therefore, no existing data suffice to test for distributed deformation in the Ethiopian Highlands or the Somali Platform. This project combines a large-aperture GPS network and a large-aperture broadband seismometer array with numerical modeling to characterize the lateral and vertical deformation patterns within the lithosphere surrounding the Main Ethiopian Rift.

The theory of plate tectonics includes continental breakup as one of its fundamental principles. In the past, continental masses have both coalesced and fractured but it is unclear how continental breakup progresses over space and time, aside from general inferences that this breakup must be very variable in heterogeneous continental materials. The East African region is the best ongoing example of a fracturing continent, but it has mostly been studied in the great rift valleys, omitting any important processes extending beyond the rift. This experiment takes a broader view of continental breakup, studying not only surface rifting, but also deformation far beyond the rift. The results have potential scientific implications for the general understanding of plate tectonics processes and of the fundamental properties of the continents. The results will also help map new geothermal energy resources, earthquake and volcano hazards, and the rise and fall of high mountains and plateaus in Africa.

National Science Foundation (NSF)
Division of Earth Sciences (EAR)
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David Fountain
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University of Oklahoma
United States
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