Relevance of Afar seismicity and volcanism to the mechanics of accreting plate boundaries

Abdallah, Anis; Courtillot, Vincent; Kasser, Michel; Dain, Anne-Yvonne Le; Lépine, Jean-Claude; Robineau, Bernard; Ruegg, Jean; Tapponnier, Paul; Tarantola, Albert

doi:10.1038/282017a0

Cited by 123 publications

(72 citation statements)

References 15 publications

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“…Both the narrow zone of subsidence within the central rift and the shoulder uplift along the length of the Dabbahu segment are consistent with the displacement field expected for a large-scale vertical dyke intrusion with induced faulting 5,12,13 . The dyke did not reach the surface along most of its length, suggesting that normal faulting occurred ahead of and/or above the laterally propagating dyke, enhancing the graben subsidence caused by the magma emplacement alone 12 .…”

Section: (Ref 9)supporting

confidence: 61%

Magma-maintained rift segmentation at continental rupture in the 2005 Afar dyking episode

Wright

Ebinger

Biggs³

et al. 2006

Nature

514

538

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Section: (Ref 9)supporting

confidence: 61%

Magma-maintained rift segmentation at continental rupture in the 2005 Afar dyking episode

Wright

Ebinger

Biggs³

et al. 2006

Nature

514

538

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“…During a two-month swarm, several thousand earthquakes were recorded, the largest with local magnitude 5.3 (ref. 44), and seismicity was observed to propagate to the southeast 44 away from a shallow (2-4 km) magma chamber identified in magnetotelluric data 45 . An extensive set of faults up to 10 km long slipped by up to 0.5 m (ref.…”

Section: Subaerial Rifting Episodes In the Modern Eramentioning

confidence: 99%

“…An extensive set of faults up to 10 km long slipped by up to 0.5 m (ref. 46), and 16 × 10 6 m 3 of basaltic lava was erupted from a 0.75-km-long fissure 44 . Geodetic measurements showed that up to 1.9 m of extension occurred across the rift 46,47 , with a 3-km-wide central graben subsiding by 70 cm and rift flanks uplifting by ~20 cm (ref.…”

Section: Subaerial Rifting Episodes In the Modern Eramentioning

confidence: 99%

Geophysical constraints on the dynamics of spreading centres from rifting episodes on land

et al. 2012

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Most of the Earth's crust is created along 60,000 km of mid-ocean ridge system. Here, tectonic plates spread apart and, in doing so, gradually build up stress. This stress is released during rifting episodes, when bursts of magmatic activity lead to the injection of vertical sheets of magma -termed dykes -into the crust. Only 2% of the global mid-ocean ridge system is above sea level, so making direct observations of the rifting process is difficult. However, geodetic and seismic observations exist from spreading centres in Afar (East Africa) and Iceland that are exposed at the land surface. Rifting episodes are rare, but the few that have been well observed at these sites have operated with remarkably similar mechanisms. Specifically, magma is supplied to the crust in an intermittent manner, and is stored at multiple positions and depths. It then laterally intrudes in dykes within the brittle upper crust. Depending on the availability of magma, multiple magma centres can interact during one rifting episode. If we are to forecast large eruptions at spreading centres, rifting-cycle models will need to fully incorporate realistic crust and mantle properties, as well as the dynamic transport of magma.

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“…Regarding the area of increased mean InSAR velocity extending eastwards towards the Dobi graben and the Mak'Arrassou region, the discrepancy between the two tracks results from the difference of total number of interferograms used for each map, confirming that the amount of deformation and/or residual tropospheric content varies within the interferograms. The strongest gradients in both GPS and InSAR velocity fields (Figs 3 and 4) occur across the Asal-Ghoubbet Rift segment, activated in November 1978 (Abdallah et al 1979), which thus accommodates a large part of the divergent Arabia/Somalia motion.…”

Section: General Description Of the Geodetic Observationsmentioning

confidence: 99%

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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Relevance of Afar seismicity and volcanism to the mechanics of accreting plate boundaries

Cited by 123 publications

References 15 publications

Magma-maintained rift segmentation at continental rupture in the 2005 Afar dyking episode

Magma-maintained rift segmentation at continental rupture in the 2005 Afar dyking episode

Geophysical constraints on the dynamics of spreading centres from rifting episodes on land

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

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