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Sub-Saharan Africa Geodetic Strain Rate Model 1.0

D.S. Stamps, E. Saria, C. Kreemer




In this report we describe the Sub-Saharan Africa Geodetic Strain Rate Model 1.0, which is a contribution to the Global Earthquake Model Foundation (GEM) Strain Rate Project. The objective of this work is to improve the latest GEM geodetic strain rate model with an updated strain rate field of sub-Saharan Africa. SubSaharan Africa encompasses the East African Rift System (EARS), the active divergent plate boundary between the Nubian and Somalian plates, which accommodates strain along the boundaries of at least 3 microplates. The current version of the GEM geodetic strain rate model is constrained by published geodetic data along the EARS and includes microplates between the Nubian and Somalian plates. In this work we developed an improved strain rate field for sub-Saharan Africa that incorporates 1) an expanded geodetic velocity field within the Nubia-Somalia plate system and along the EARS 2) redefined regions of deforming zones guided by seismicity distribution, and 3) updated constraints on block rotations from the recent publication of Saria et al. (2014). The Sub-Saharan Africa Geodetic Strain Rate Model 1.0 spans longitudes 22 to 55.5 and latitudes -52 to 20 with 0.5° (longitude) by 0.4° (latitude) spacing, which includes part or all of the following plates and/or sub-plates: Somalia, Nubia, Rovuma, Lwandle, Victoria, Antarctica, and Arabia. For these plates/sub-plates we assign rigid block rotations as boundary constraints on the strain rate calculation that is determined using the Haines and Holt method of fitting splines to geodetic data for an interpolated velocity gradient tensor field. We derive strain rates, velocities, and vorticity rates from the velocity gradient tensor field. Following the work of Kreemer et al. 2014 for the GEM geodetic strain rate field we also provide estimates of model uncertainties, velocities, vorticity, and strain rates in a Nubia-fixed reference frame relative to the lower mantle for a 0.1° x 0.1° mesh.

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