We analyzed 16 years of GPS and 17 years of Doppler orbitography and
radiopositioning integrated by satellite (DORIS) data at continuously operating geodetic
sites in Africa and surroundings to describe the present-day kinematics of the Nubian and
Somalian plates and constrain relative motions across the East African Rift. The resulting
velocity field describes horizontal and vertical motion at 133 GPS sites and 9 DORIS
sites. Horizontal velocities at sites located on stable Nubia fit a single plate model with a
weighted root mean square residual of 0.6 mm/yr (maximum residual 1 mm/yr), an upper
bound for plate-wide motions and for regional-scale deformation in the seismically active
southern Africa and Cameroon volcanic line. We confirm significant southward motion
(1.5 mm/yr) in Morocco with respect to Nubia, consistent with earlier findings. We
propose an updated angular velocity for the divergence between Nubia and Somalia,
which provides the kinematic boundary conditions to rifting in East Africa. We update a
plate motion model for the East African Rift and revise the counterclockwise rotation of
the Victoria plate and clockwise rotation of the Rovuma plate with respect to Nubia.
Vertical velocities range from –2 to +2 mm/yr, close to their uncertainties, with no clear
geographic pattern. This study provides the first continent-wide position/velocity solution
for Africa, expressed in International Terrestrial Reference Frame (ITRF2008), a
contribution to the upcoming African Reference Frame (AFREF). Except for a few
regions, the African continent remains largely under-sampled by continuous space
geodetic data. Efforts are needed to augment the geodetic infrastructure and openly share
existing data sets so that the objectives of AFREF can be fully reached.
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