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

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.