Integrated geological and geophysical analysis of the active Sidi–Thabet fault in northeastern Tunisia: insights into recent deformation and seismotectonic implications

Abstract

The Sidi-Thabet fault, a key structure within the Atlas-Tell orogenic belt in northern Tunisia, illustrates the complex interplay between inherited Tethyan extensional features and subsequent compressional deformation during Tertiary African-Eurasian plate convergence. This study provides insights into the recent activity and seismotectonic significance of the fault by combining geological mapping, shallow geophysical surveys and morphotectonic analysis with seismic and focal mechanism studies. Steeply dipping fault planes, brittle fracture zones and vertical displacements affecting Quaternary and Cretaceous strata are evident from seismic refraction and electrical resistivity tomography. The evidence for recent fault reactivation is further supported by morphotectonic markers. These include displaced calcrete beds, fresh scarps, and disrupted landforms. The focal mechanism analysis indicates a predominantly compressional tectonic regime with secondary normal faulting. This emphasizes that this fault accommodates both transpressional shortening and vertical uplift along its segmented trace. The presence of ductile salt layers enhances deformation complexity, driving differential uplift and influencing the architecture of fault-related folds. These results confirm that the Sidi-Thabet Fault is a major zone of active deformation within the Tunisian Atlas, emphasizing its critical role in seismic hazard assessment, especially given its proximity to Tunis, a city of three million people located just south of the fault.