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The evolving deformation field in central Afar from two decades of InSAR observations: Implications for the decoupling between the upper and lower crusts
  • Simran Sangha,
  • Gilles Peltzer,
  • Cécile Doubre
Simran Sangha
University of California Los Angeles

Corresponding Author:simran.s.sangha@jpl.nasa.gov

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Gilles Peltzer
University of California Los Angeles
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Cécile Doubre
IPGS-EOST
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Abstract

Located at the meeting point between the Red Sea Ridge, the East African Rift and the Aden Ridge, the Afar Depression is characterized by contrasting modes of deformation with focused extension across recently activated magmatic segments and broadly distributed faults. InSAR data spanning over two decades reveal stable and evolving patterns in the deformation field of Central Afar, including (1) a 120 km-wide belt of horizontal extension, extending from west to east between the Manda-Hararo and Asal-Ghoubbet rifts and accommodating ~12 mm/yr of the Arabia-Somalia plate motion, (2) broad zones of subsidence aligned with the axial volcanic ridges marking the major diverging segments propagating into Afar, (3) accelerated opening and uplift across the Manda-Hararo Rift subsequent to the 2005-2010 diking sequence, and (4) a series of four micro-faulting events, which occurred between 2001 and 2005 on an alignment of north-northeast trending rifts between the Afdera and Gad Elu volcanoes. These observations suggest that different modes of deformation take place in the shallow and deeper parts of the crust, which are mechanically decoupled. Major magmatic segments steadily opening into the deep part of the crust between diking episodes, produce focused extension and plate thinning at intermediate depth, resulting in localized subsidence along axial ridges. The horizontal diverging movement across the segments is transformed by creep in a detachment fault at the base of the brittle crust, which deforms by distributed faulting. Episodic emplacements of dikes above deep-seated diverging segments compensate for inter-diking subsidence, also accommodating extension in the shallow crust.