Seismotectonics and Crustal Shortening Evidence beneath the Intraplate Western High Atlas, Morocco: Insights from Earthquake Relocation, Focal Mechanisms, and Stress Inversion

Abstract

The High Atlas Mountains constitute a major intracontinental orogen shaped by the long-term convergence between the Nubian and Eurasian plates. However, the present-day seismotectonic deformation and stress regime of the Western High Atlas remains insufficiently constrained. Here, we analyze relocated earthquakes recorded between 2014 and 2023, with local magnitudes ranging from 3.3 to 6.8, along with focal mechanism solutions and stress tensor inversion, to develop an updated seismotectonic interpretation of the Western High Atlas and to better constrain the mechanisms governing crustal deformation. The focal mechanism solutions indicate a predominance of oblique-reverse faulting, with secondary strike-slip and local normal components. Stress tensor inversion yields a nearly horizontal, approximately N-S to NNW-SSE oriented maximum compressive stress axis (σ1), consistent with the inferred regional SHmax direction. These results support active compressional to transpressive deformation within the Western High Atlas and suggest that crustal shortening is partly accommodated by the reactivation of inherited structures. The results indicate that strain partitioning is controlled by the interaction between far-field Nubia-Eurasia convergence and local crustal heterogeneities. This study provides new constraints on the active tectonic framework of the Western High Atlas and contributes to seismic hazard assessment in this intraplate mountain belt.