Aseismic creep and strain partitioning accommodating the Nubia-Eurasia oblique convergence in northern Africa from InSAR analysis

Abstract The northern Africa region faces significant seismic and tsunami hazards, driven by the ongoing convergence between the Nubian and Eurasian plates. Using radar interferometry (interferometric synthetic aperture radar, InSAR) analysis, we provide constraints on the interseismic behavior of tectonic structures within the region between ~2°W and ~11°E using the first InSAR-derived regional-scale maps of east-west and vertical velocity components. Despite the unresolved N-S–oriented motions due to inherent limitations to the InSAR technique, our millimeter-per-year level velocity maps reveal three distinct domains of strain accommodation along the plate boundary. In Western Tell, both onshore and offshore folds and thrusts accommodate frontal collision, regularly generating large reverse earthquakes, such as the Ms 7.3 El Asnam earthquake of 1981. In the Eastern Tell, deformation is widely distributed from the Saharan Platform to the northern coastlines. In the Central Tell, we identify the predominantly aseismic behavior of the 500-km-long Ghardimaou-North-Constantine fault, marked by a shallow locking depth (<5.1 ± 0.5 km) and standing out as one of the slowest (<2.5 mm/yr) continental strike-slip faults ever detected with geodetic data. Strain partitioning diverts most of the shear component of the oblique convergence into this major inland structure, thereby making the offshore thrusts and folds the principal sources of seismic hazard.