Continental rifts begin and develop through repeated episodes of faulting and magmatism, but strain partitioning between faulting and magmatism during discrete rifting episodes remains poorly documented. In highly evolved rifts, tensile stresses from far-field plate motions accumulate over decades before being released during relatively short time intervals by faulting and magmatic intrusions1,2,3. These rifting crises are rarely observed in thick lithosphere during the initial stages of rifting. Here we show that most of the strain during the July–August 2007 seismic crisis in the weakly extended Natron rift, Tanzania, was released aseismically. Deformation was achieved by slow slip on a normal fault that promoted subsequent dyke intrusion by stress unclamping. This event provides compelling evidence for strain accommodation by magma intrusion, in addition to slip along normal faults, during the initial stages of continental rifting and before significant crustal thinning.

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Envisat/ASAR data were systematically programmed and acquired through the ESA Cat-1 project no. C1P.3224. Interferograms were computed using DORIS software (Delft University of Technology). Precise orbits were provided by the Delft Institute of Earth Observation and Space Systems and ESA. We thank the Tanzania Survey and Mapping Department for their support of the October field expedition and the Tanzania Commission for Science and Technology. We thank V. Cayol and Y. Fukushima for their contribution in analysing the ground deformations, F. Paganelli, J. Biggs and J. Keller for discussions and K. Feigl and F. Sigmundsson for their comments. We acknowledge support from the US National Science Foundation under grants EAR-0801801 and EAR-0538119, from the French INSU-CNRS DyETI programme and from the Belgian Science Policy under projects SAMAAV and Rukwa.

Author Contributions N.d’O., A.O. and F.K. planned the radar data acquisition and computed the interferograms; J.A., A.D., J.D., R.W.F. and J.P. designed the seismic experiment and collected and analysed the resulting data; D.D., A.S.M., B.S. and C.W. performed the field observations; E.S. and D.S.S. deployed the GPS equipment and processed the resulting data; C.E. provided tectonic context; E.C. performed the model calculations; E.C. and N.d’O. wrote the paper. All authors discussed the results and commented on the manuscript.

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  1. Purdue University, Department of Earth and Atmospheric Sciences, West Lafayette, Indiana 47906, USA

    • Eric Calais
    •  & D. Sarah Stamps
  2. National Museum of Natural History, Department of Geophysics/Astrophysics, L-2160 Luxembourg

    • Nicolas d’Oreye
    •  & Anneleen Oyen
  3. Institut Universitaire Européen de la Mer, Université de Bretagne Occidentale, Plouzané 29280, France

    • Julie Albaric
    • , Jacques Déverchère
    •  & Julie Perrot
  4. Géosciences Azur, UNS/CNRS, Valbonne 06560, France

    • Anne Deschamps
  5. Royal Museum for Central Africa, Tervuren 3080, Belgium

    • Damien Delvaux
    • , François Kervyn
    • , Benoît Smets
    •  & Christelle Wauthier
  6. University of Rochester, Department of Earth and Environmental Sciences, New York, New York 14627, USA

    • Cynthia Ebinger
  7. University of Dar es Salaam, Department of Geology, PO Box 35091, Dar es Salaam, Tanzania

    • Richard W. Ferdinand
  8. Renard Centre of Marine Geology, Department of Geology and Soil Science, Universteit Gent, Gent 9000, Belgium

    • Athanas S. Macheyeki
  9. Mineral Resources (Madini) Institute, PO Box 903, Dodoma, Tanzania

    • Athanas S. Macheyeki
  10. Delft University of Technology, Delft 2600, The Netherlands

    • Anneleen Oyen
  11. Ardhi University, Department of Geomatics, PO Box 35176, Dar es Salaam, Tanzania

    • Elifuraha Saria
  12. University of Liège, Liège 4000, Belgium

    • Christelle Wauthier


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Correspondence to Eric Calais.

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