Present‐day kinematics of the East African Rift

Abstract

The East African Rift (EAR) is a type locale for investigating the processes that drive continental rifting and breakup. The current kinematics of this ∼5000 km long divergent plate boundary between the Nubia and Somalia plates is starting to be unraveled thanks to a recent augmentation of space geodetic data in Africa. Here we use a new data set combining episodic GPS measurements with continuous measurements on the Nubian, Somalian, and Antarctic plates, together with earthquake slip vector directions and geologic indicators along the Southwest Indian Ridge to update the present-day kinematics of the EAR. We use geological and seismological data to determine the main rift faults and solve for rigid block rotations while accounting for elastic strain accumulation on locked active faults. We find that the data are best fit with a model that includes three microplates embedded within the EAR, between Nubia and Somalia (Victoria, Rovuma, and Lwandle), consistent with previous findings but with slower extension rates. We find that earthquake slip vectors provide information that is consistent with the GPS velocities and helps to significantly reduce uncertainties of plate angular velocity estimates. We also find that 3.16 Myr MORVEL average spreading rates along the Southwest Indian Ridge are systematically faster than prediction from GPS data alone. This likely indicates that outward displacement along the SWIR is larger than the default value used in the MORVEL plate motion model.

Current deformation in Central Afar and triple junction kinematics deduced from GPS and InSAR measurements

“…As shown by Kogan et al (2012) and Birhanu et al (2016), the stations located in the southeastern part of the network (BILA, DAMY, ARBK and BKOB) show NE-trending horizontal velocities. That differs from the N090-110 • E-trending velocity expected by the present-day plate models (Déprez et al 2013(Déprez et al , 2015Saria et al 2013Saria et al , 2014Fig. 4).…”

“…Regarding the GPS data, only the horizontal baseline between the sites of OLAB and BKOB, located ∼50 and ∼160 km away from the rift axis, respectively, can be used to quantify the extension rate. Projected along a ∼N100 • E trending profile, that is perpendicular to the rift axis, the opening rate is ∼3 mm yr -1 , which is lower than the opening rate predicted by the plate motion models at this latitude of the EAR (∼5 mm yr -1 along the N100 • E direction, Chu & Gordon 1999;Déprez et al 2013Déprez et al , 2015Saria et al 2014). As shown by Kogan et al (2012) and Birhanu et al (2016), the stations located in the southeastern part of the network (BILA, DAMY, ARBK and BKOB) show NE-trending horizontal velocities.…”

Surface wave imaging of the weakly extended Malawi Rift from ambient-noise and teleseismic Rayleigh waves from onshore and lake-bottom seismometers

“…Furthermore, data from a single GPS within the Malawi Rift estimate a plate-opening velocity of ca. 1 mm yr −1 (Saria et al 2014).…”

Lithospheric low-velocity zones associated with a magmatic segment of the Tanzanian Rift, East Africa

“…The NE-trending Eyasi-Wembere rift arm cross-cuts the east of the suture of the Pan-African-Archaean boundary and continues further SW across the deeply rooted craton. From geodetic data, direction of plate separation in East Africa are estimated at 4 mm yr −1 in an approximately E-W direction (Saria et al 2014).…”