Stress field variations along the Maghreb region derived from inversion of major seismic crisis fault plane solutions

This study is devoted to the analysis of the stress state along the Maghreb region based on the inversion of focal solutions. We have inverted the main shock and aftershock focal mechanisms of the strongest seismic events that occurred in five seismogenic zones, from west to east: Al Hoceima (2004), Cheliff (1980), Tipasa-Chenoua (1989), Zemmouri (2003) and Constantine (1985). Most of the focal mechanisms of the aftershock sequences have been constructed within this study. Compressive stress regime is observed in the central part of Algeria between Cheliff and Zemmouri. On both edges of the Maghreb region, the stress regime becomes strike-slip in the Constantine region and in the Moroccan Rift. These different regimes seem to be linked to the free-edge effect (Ionian slab subduction) and to the dynamics of the Alboran Sea in the eastern and western parts of the study area respectively. The σ1 directions experience an anticlockwise rotation of about 20° from eastern to central Algeria. We observe that the direction of σ1 and the direction of convergence are the closest in central Algeria, where the collision is not perturbed by edge effect.