Abstract
AbstractStudying the mechanisms of interaction between rift segments is key to understanding the kinematics of plate boundaries in continental rifts. However, the spatial and temporal evolution of deformation at rift linkage zones is rarely observed directly. Here, we combine InSAR data spanning 2005–2010 and 2014–2019 from ENVISAT and Sentinel‐1 satellites, respectively, with local seismicity from the Afar rift to investigate the plate‐boundary kinematics of the Afrera linkage zone, the junction between the Erta Ale and Tat Ali magmatic segments in Northern Afar (Ethiopia). We obtain time‐series of cumulative InSAR Line‐Of‐Sight (LOS) displacements that show deformation is accommodated by a series of active en‐echelon faults striking ∼NS and characterized by normal slip associated with a left‐lateral strike‐slip component. Additionally, we observe spatial variation in fault behavior with stick‐slip and creep. The faults in the center of the linkage zone behave primarily in a stick‐slip mode (with abrupt fault displacements up to ∼40 mm) and fault motions are associated with earthquakes of ML > 5. Conversely, faults at the edge of the linkage zone, near the magmatic segments, show creep and some stick‐slip behavior (with cumulative LOS displacement up to ∼30–40 mm over a ∼5‐year period) accompanied by low‐level seismicity. Some of the creeping faults are also spatially associated with hydrothermal springs. We interpret that the temporal behavior of the faults in the linkage zone is controlled by the interplay between tectonic extension, high heat flows, and fluid circulation near the magmatic segments where creeping of some faults is favored.
Highlights
During continental rupture, the plate-boundary zone is segmented along its length to form discrete rift segments which accommodate plate divergence through tectonic and magmatic activity (Hayward & Ebinger, 1996; Keir et al, 2009; Manighetti et al, 2001)
Numerical modeling, field observations, and geodetic measurements suggested that the Afrera Plain is an active linkage zone between the Erta Ale and Tat Ali rift segments, but whether this linkage zone may evolve into a transform fault is still debated (Bonatti et al, 2017; Illsley-Kemp et al, 2018; La Rosa et al, 2019)
We provided one of the few direct observations on how deformation is distributed across a linkage zone between two active magmatic segments
Summary
The plate-boundary zone is segmented along its length to form discrete rift segments which accommodate plate divergence through tectonic and magmatic activity (Hayward & Ebinger, 1996; Keir et al, 2009; Manighetti et al, 2001). Numerical modeling, field observations, and geodetic measurements suggested that the Afrera Plain is an active linkage zone between the Erta Ale and Tat Ali rift segments, but whether this linkage zone may evolve into a transform fault is still debated (Bonatti et al, 2017; Illsley-Kemp et al, 2018; La Rosa et al, 2019). A recent study by La Rosa et al (2019) used InSAR, seismicity, and structural geology to investigate a fault slip in Afrera associated with a ML 5.0 in 2007 and proposed a model of rift linkage consisting of a right-lateral, NW-SE-trending transfer zone where deformation is accommodated by dominant ∼NS-striking faults with oblique kinematics characterized by both normal and left-lateral components (Figure 1). We document how creep and stick-slip are partitioned across the Afrera linkage zone and observe that creeping faults are located in proximity to the active magmatic segments and hydrothermal springs, suggesting that the creeping fault behavior could be controlled by high heat flows and hydrothermal fluids circulation
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