The evolving deformation field in central Afar from two decades of InSAR
observations: Implications for the decoupling between the upper and
lower crusts
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.