The 8 September 2023 High Atlas, Morocco, Earthquake: Fault Geometry and Seismic Image of the Source Zone

The M_w 6.8 thrust faulting earthquake of 8 September 2023 is the most destructive event in Morocco over the past decade. This earthquake took place in the Al Haouz region, situated in the western part of the High Atlas (HA) domain. The Atlas Mountains are recognized as a slowly deforming mountain belt based on active tectonics and Global Navigation Satellite Systems data, with seismic activity that remains poorly understood. To better understand the cause of this major earthquake, we analyzed P-and S-wave arrivals at 14 regional seismic stations. This analysis has enabled the creation of a high-resolution 3D velocity structure of the seismic zone and the western section of the HA. The results indicate that the mainshock centroid depth is at approximately 24 km, located within fractured rock formations characterized by a low P-wave velocity zone that extends from 10 to 45 km depth. The Interferometric Synthetic Aperture Radar (InSAR) technique was also employed to identify the coseismic deformation zone, revealing that the maximum slip occurred at a depth of 25 km. Aftershock relocations, determined using the double-difference method along with the seismicity distribution, suggest a fault rupture geometry consistent with the InSAR model and the tomographic image of the earthquake zone. These results identified an east-northeast–west-southwest-trending, north-northwest-dipping thrust fault along the southern front of the High Atlas (HA).