Quaternary slip rates and seismic hazard of the Gafsa intraplate fault system (southern Atlas, Tunisia)

Raouf Ghribi¹, Hassene Affouri², Rouaida Trabelsi¹ & Adel Rigane^1
1L.R. Modélisation des Systèmes Géologiques et Hydrologiques (GEOMODELE) LR/16/ES17 BP1171, Department of Earth Sciences, Faculty of Sciences of Sfax, University of Sfax, Tunisia.
²L.R. Géoressources, Matériaux, Environnements et changements globaux (GEOGLOB), LR/13/ES23 BP1171, Department of Earth Sciences, Faculty of Sciences of Sfax, University of Sfax, Tunisia.
Corresponding author e-mail: raouf.ghribi@fss.usf.tn

Displaced and well-preserved Quaternary landforms, such as terrace risers and offset-beheaded streams, provide evidence of active intraplate deformation along the Gafsa Fault system. Their northern and southern Sidi Ahmed Zeroug Fault Strands (NSAZF and SSAZF) exhibit a complex history of right-lateral strike-slip and dip-slip motion within the Southern Tunisian Atlas located hundreds of kilometers away from the active African-Eurasian plate boundary. Geomorphic analysis of displaced stream channels along the SSAZF reveals a most recent earthquake offset of 3-4 m, with cumulative offsets reaching up to 35 m, corresponding to approximately 4 m per seismic event. Slip rate estimations indicate a Late Pleistocene right-lateral displacement rate of 3.53 mm/year along the NSAZF, which decreases by 60% in the Holocene to 1.44 mm/year. The vertical slip rate for the NSAZF is 0.13 mm/year in the Late Pleistocene, increasing to 0.21-0.34 mm/year in the Holocene, likely due to intensified regional compressive stress. The SSAZF exhibits nearly equal lateral and vertical slip rates, averaging 0.35-0.37 mm/year. Structural complexities such as restraining bends and secondary NW-oriented faults contribute to variations in slip distribution. Seismic hazard analysis suggests that the Gafsa Fault system is capable of generating earthquakes with a maximum moment magnitude of M6.7±0.2, with an estimated recurrence interval of 300-5000 years. These findings provide critical insights into the neotectonic activity of the study region and its implications for seismic hazard assessment.

lateral and vertical slip rates, displaced Quaternary features, seismic hazard, active Gafsa Fault, Southern Tunisian Atlas.