12/4/2013 - Evidence of Rift-Parallel Deformation Along the Western Branch and Main Ethiopian Rift?


12:00 PM - 1:00 PM
Geology 1707

Presented By:
Dr. Sarah Stamps - MIT


The East African Rift System spans N-S ~5000 km and currently experiences E-W extension. Previous kinematic studies of the EARS delineated 3 relatively rigid sub-plates (Victoria, Rovuma, and Lwandle) between the Nubian and Somalian plates. GPS observations of these block interiors confirm the rigid plate model, but new observations within individual rifts are beginning to show deformation that does not conform to large-scale E-W extension. Here we present (1) new velocity solutions based on GPS observations within the Main Ethiopian Rift, the southern Albertine Rift, and the Rungwe Volcanic Province, (2) a kinematic model for the Rwenzori block in the northern Western Branch and (3) preliminary work aimed at deciphering non-volcanic deformation within the Rungwe Volcanic Province such that we can detect the long-term tectonic deformation signal. Our velocity solutions suggest a possible systematic rift-parallel deformation pattern that has previously been undetected due to a lack of geodetic observations. We find that the existing kinematic models of the EAR are unable to explain the along-rift deformation, thus we developed a new kinematic model that includes the Rwenzori block within the Western Branch constrained by GPS observations and earthquake slip vectors derived from a local seismic network. Our early work suggests the Rwenzori block rotates clockwise relative to the Victoria block. Further south in the Rungwe Volcanic Province, we investigate a pre-2011 volcanic eruption velocity field to test the hypothesis of systematic along-rift deformation. Preliminary results indicate a possible inflation event prior to the 2011 volcanic eruption that must be removed from the pre-2011 volcanic eruption velocity field, from which we then observe rift-parallel deformation. Our work demonstrates the kinematics of individual rifts needs to be re-evaluated in the broader context of the East African Rift System.

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