Lithospheric strength and strain localization in continental extension from observations of the East African Rift

Kogan, Lewis; Fisseha, Shimeles; Bendick, Rebecca; Reilinger, Robert; McClusky, S.; King, Robert W.; Solomon, Theodros

doi:10.1029/2011jb008516

Cited by 98 publications

(153 citation statements)

References 144 publications

(236 reference statements)

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“…At large scale, the GPS velocities are consistent with the far field plate motion deduced from tectonic models, except for the northern part of the Somalia plate, where the vectors show a NE trending motion from low latitudes, in agreement with the observations of Kogan et al (2012) and Birhanu et al (2016) that were made across the Central MER. This suggests that the northern part of the Somalia plate evolves independently from the whole Somalia plate, whose motion is determined from GPS stations mainly located in the Southern Hemisphere.…”

Section: O N C L U S I O N Ssupporting

confidence: 86%

“…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. 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.…”

Section: The Northern Part Of the Main Ethiopian Riftmentioning

confidence: 79%

“…McClusky et al (2010) focused on the motion of the Danakil block and its consequences on the total Kinematics of the Afar triple junction 939 amount of extension within the AD. Kogan et al (2012) examined the evolution of the velocities with respect to Nubia from the western high plateaus to the RS. However, the density of measurements in this area is too low to precisely quantify the respective role of these basins in the accommodation of the Arabia/Africa divergent motion.…”

Section: Plio-pleistocene Deformation In Central Afarmentioning

confidence: 99%

“…Table 1 presents the dates of measurements for each site. In addition to measurements available on the UNAVCO website (Calais & Buck 2007;Calais 2008Calais , 2009Nooner et al 2009;Kogan et al 2012;Hamling et al 2014;Pagli et al 2014) and on the French GPS archive website GPScope Table 1. Location, magnitude of velocity components with respect to Nubia fixed (Déprez et al 2015), dates of measurements for the sites in Afar.…”

Section: Gpsmentioning

confidence: 99%

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

Doubre¹,

Déprez²,

Masson³

et al. 2016

Geophys. J. Int.

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S U M M A R YKinematics of divergent boundaries and Rift-Rift-Rift junctions are classically studied using long-term geodetic observations. Since significant magma-related displacements are expected, short-term deformation provides important constraints on the crustal mechanisms involved both in active rifting and in transfer of extensional deformation between spreading axes. Using InSAR and GPS data, we analyse the surface deformation in the whole Central Afar region in detail, focusing on both the extensional deformation across the Quaternary magmato-tectonic rift segments, and on the zones of deformation transfer between active segments and spreading axes. The largest deformation occurs across the two recently activated Asal-Ghoubbet (AG) and Manda Hararo-Dabbahu (MH-D) magmato-tectonic segments with very high strain rates, whereas the other Quaternary active segments do not concentrate any large strain, suggesting that these rifts are either sealed during interdyking periods or not mature enough to remain a plate boundary. Outside of these segments, the GPS horizontal velocity field shows a regular gradient following a clockwise rotation of the displacements from the Southeast to the East of Afar, with respect to Nubia. Very few shallow creeping structures can be identified as well in the InSAR data. However, using these data together with the strain rate tensor and the rotations rates deduced from GPS baselines, the present-day strain field over Central Afar is consistent with the main tectonic structures, and therefore with the long-term deformation. We investigate the current kinematics of the triple junction included in our GPS data set by building simple block models. The deformation in Central Afar can be described by adding a central microblock evolving separately from the three surrounding plates. In this model, the northern block boundary corresponds to a deep EW-trending trans-tensional dislocation, locked from the surface to 10-13 km and joining at depth the active spreading axes of the Red Sea and the Aden Ridge, from AG to MH-D rift segments. Over the long-term, this plate configuration could explain the presence of the en-échelon magmatic basins and subrifts. However, the transient behaviour of the spreading axes implies that the deformation in Central Afar evolves depending on the availability of magma supply within the well-established segments.

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Section: O N C L U S I O N Ssupporting

confidence: 86%

Section: The Northern Part Of the Main Ethiopian Riftmentioning

confidence: 79%

Section: Plio-pleistocene Deformation In Central Afarmentioning

confidence: 99%

Section: Gpsmentioning

confidence: 99%

See 2 more Smart Citations

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

Doubre¹,

Déprez²,

Masson³

et al. 2016

Geophys. J. Int.

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“…The southward increase in seismic moment release and shift in seismicity from axial volcanic segments to border faults is concomitant with a significant decrease in overall vent density. These coupled observations suggest that extension in the southern MER is accommodated mainly by faulting on border faults, an interpretation supported by GPS measurements showing that extension in southern MER is localised mainly to the western border fault (Kogan et al, 2012). The along-rift variation in number and distribution of large magnitude earthquakes coupled with the distribution of major volcanic centres suggests that border faulting accommodates a significant proportion of strain in the southern MER.…”

Section: Spatial Distributionmentioning

confidence: 63%

Spatial relationship between earthquakes and volcanic vents in the central-northern Main Ethiopian Rift

Mazzarini

Keir

Isola

2013

Journal of Volcanology and Geothermal Research

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During the breakup of continents extension is commonly accommodated by connected networks of fluid filled fractures (dykes) and by faults. Despite the importance of these two extension mechanisms their spatial relationship in three dimensions is poorly understood primarily because it is difficult to quantify the subsurface distribution of faulting and intrusion. In order to address this problem, we conduct a quantitative analysis of the spatial distribution and clustering of earthquakes and volcanic vents in the Main Ethiopian Rift in East Africa in order to understand how extension by faulting and intrusion is distributed throughout the volcanic rift. We use fractal analysis of earthquake epicentres in order to infer the 2D characteristics of the subsurface fault network, and directly test our model results against the 3D distribution of earthquake hypocentres. Our results show that fractal analysis of these features is a reliable means to characterise the 3D properties of the fault network. In addition, the strong similarity between the properties of the fault network derived from earthquakes and properties of the magma-filled fracture network derived from fractal analysis of volcanic vents strongly suggests that these are genetically linked. We then explore their spatial link using computation of earthquake and vent density, which shows that the zone of seismicity is generally around 20-30-km-wide, while the zone of vents is narrower and centred within the zone of seismicity. This spatial relationship suggests that the faults, which form rift axial grabens, are induced above a narrower and central zone of diking. We also demonstrate significant along-rift variation in degree of magmatism and faulting with regions of increased degree of diking inferred from a higher cone density characterised by reduced degree of faulting.

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Current kinematics and dynamics of Africa and the East African Rift System

et al. 2014

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Although the East African Rift System (EARS) is an archetype continental rift, the forces driving its evolution remain debated. Some contend buoyancy forces arising from gravitational potential energy (GPE) gradients within the lithosphere drive rifting. Others argue for a major role of the diverging mantle flow associated with the African Superplume. Here we quantify the forces driving present‐day continental rifting in East Africa by (1) solving the depth averaged 3‐D force balance equations for 3‐D deviatoric stress associated with GPE, (2) inverting for a stress field boundary condition that we interpret as originating from large‐scale mantle tractions, (3) calculating dynamic velocities due to lithospheric buoyancy forces, lateral viscosity variations, and velocity boundary conditions, and (4) calculating dynamic velocities that result from the stress response of horizontal mantle tractions acting on a viscous lithosphere in Africa and surroundings. We find deviatoric stress associated with lithospheric GPE gradients are ∼8–20 MPa in EARS, and the minimum deviatoric stress resulting from basal shear is ∼1.6 MPa along the EARS. Our dynamic velocity calculations confirm that a force contribution from GPE gradients alone is sufficient to drive Nubia‐Somalia divergence and that additional forcing from horizontal mantle tractions overestimates surface kinematics. Stresses from GPE gradients appear sufficient to sustain present‐day rifting in East Africa; however, they are lower than the vertically integrated strength of the lithosphere along most of the EARS. This indicates additional processes are required to initiate rupture of continental lithosphere, but once it is initiated, lithospheric buoyancy forces are enough to maintain rifting.

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Lithospheric strength and strain localization in continental extension from observations of the East African Rift

Cited by 98 publications

References 144 publications

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

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

Spatial relationship between earthquakes and volcanic vents in the central-northern Main Ethiopian Rift

Current kinematics and dynamics of Africa and the East African Rift System

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