Proceedings of the 12th International INQUA meeting on paleoseismology, active tectonic and archaeoseismology

Fig. 2: Image depicts a fault-related fold affecting Quaternary layers on the SARF's northern limb. This small-scale observation reflects the larger-scale structural pattern of the SARF (see Fig. 6b), providing insight into the mechanics of active, fault-related folding in this area. Evidence of Active faulting and folding The SARF exhibits compelling evidence for ongoing faulting along all three segments. Upper Pleistocene layers are actively folded, displaying steep dips alongside older Plio-Quaternary units. The most striking observation is at the northern coastal terminus, where the Lower Therynian marine terrace (10 m elevation) displays a significant 60° tilt and submerges below sea level (Fig. 3) This suggests the possible offshore continuity of the SARF (Fig. 1b). Fig. 3: Field image showing the Lower marine terrace (10 meters) tilted at a high angle due to the ongoing activity of the Arzew Saline Fault-related Fold (SARF). The involvement of the latest Quaternary deposits of the Arzew Salt Lake at the SARF junction is another evidence of recent activity. Additionally, extrados normal faults affecting Holocene layers (recent reddish soil) are observed at multiple points on the extrados and along the northern limb of the SARF (Fig. 3). Geomorphic evidence further corroborates recent activity. The SARF fold geometry directly influences the well-developed Quaternary marine terraces, causing their originally flat profiles to mimic the fold's geometry (Benbakhti et al., 2018). Triangular facets are well-developed along the southwestern limb, and freshly preserved fault scarps transect Upper Quaternary deposits along the central and southern segments, with a prominent scarp traceable for several kilometers and an average height of 2 meters (Fig. 6a). R E F E R E N C E S Benbakhti, I . M., Maouche, S., Belhai, D., Harbi, A., Ritz, J. F., Rabai, G., et al. (2018). Characterizing the active tectonics in the Oran region (Algeria) and recasting the 1790 earthquake. Journal of Seismology. https: //doi. org/10.1007/s10950-018-9784-3 Bougrine, A., Yelles-Chaouche, A. K., & Calais, E. (2019). Active deformation in Algeria from continuous GPS measurements. Geophysical Journal International, 217(1), 572–588. https: //doi.org/10.1093/gji/ggz035 Bouhadad, Y. (2001). The Murdjadjo, Western Algeria, fault- related fold: Implications for seismic hazard. Journal of Seismology, 5(4), 541–558. https: //doi. org/10.1023/A: 1012039900248