Active Faulting and Stress regime in the High Atlas: New Seismological Insights

Summary The devastating Al Haouz earthquake (Mw 6.8) of September 8, 2023, highlighted the seismic risk in Morocco’s High Atlas Mountains. This study investigates the region’s present-day seismotectonic setting, focusing on the earthquake’s source area. We analyze over twenty moderate seismic events (Mw 3.5–7.0). recorded by Moroccan and international networks from 2009–2024. High-resolution data from networks operating since 2008 enable precise earthquake relocation. We compare initial locations based on P-wave arrivals with refined locations obtained using the double-difference method, which minimizes common path effects and improves relative location accuracy. This approach yields more tightly clustered hypocenters and reduces location uncertainties by 20%. The relocated earthquake hypocenters are predominantly at depths shallower than 30 km, indicating that regional seismic activity originates mostly within the upper crust. Focal mechanisms, calculated using P-wave polarities and refined via moment tensor inversion, reveal predominantly reverse faulting, with some strike-slip components. Stress tensor inversion of these mechanisms yields a N-S trending maximum horizontal stress (σ1) in the Western High Atlas, aligning with the Al Haouz fault plane orientation. This detailed analysis provides crucial insights into the ongoing deformation and seismic hazard in the High Atlas, particularly relevant after the recent event.