Anomalous far field ground subsidence induced by the 2023 Mw 6.8 Morocco earthquake

• A moderate earthquake triggered far-field subsidence 50 km from the epicenter. • The anomalous subsidence observed can be explained by shallow fault slow slip. • Combined seismic stress and groundwater pumping amplified post-seismic deformation. • Seismic hazard zones must now include vulnerable aquifers. On September 8, 2023, an Mw 6.8 earthquake struck the High Atlas Mountains southwest of Marrakesh, Morocco, causing extensive damage and loss of life. Beyond its devastating near-field effects, the earthquake also triggered unexpected far-field deformation anomalies in Oulad Berhil, approximately 50 km from the epicenter—challenging conventional seismic impact models that typically emphasize near-field responses. This study combines satellite radar time-series analysis, fault slip modeling, and Coulomb stress change (ΔCFS) calculations to investigate the mechanisms responsible for these anomalous post-seismic deformations. Prior to the earthquake, Oulad Berhil experienced persistent subsidence (∼4 cm/year), attributed to long-term groundwater over-extraction. However, deformation rates accelerated markedly following the earthquake, indicating a significant perturbation to the region’s pre-existing subsidence regime. ΔCFS modeling reveals considerable stress loading (up to 0.5 bar) on a shallow fault beneath Oulad Berhil, likely inducing aseismic slip at depths of 2–7 km, with a maximum slip of 0.345 m—equivalent to an Mw 5.6 event. In parallel, intensified groundwater withdrawal associated with post-seismic reconstruction may have contributed to the deformation, evidenced by abrupt changes of vegetation index. While the relative contributions of stress transfer and groundwater extraction remain uncertain due to data limitations, both mechanisms warrant careful monitoring. These findings demonstrate that moderate-magnitude earthquakes can destabilize distant regions through far-field fault reactivation and anthropogenic interactions, underscoring the importance of incorporating far-field stress effects into seismic hazard assessments, especially in areas experiencing active subsidence or groundwater exploitation.