Investigating seismic and aseismic fault motion caused by the 2024-2025 Fentale dyke intrusions in Ethiopia

The faulting caused by dyke intrusions provide a novel opportunity to study the way natural fault systems respond to time-varying changes to the stress field. The recent 2024-2025 Fentale-Dofen dyking episode in the northern Main Ethiopian Rift (NMER) offers a rare opportunity to investigate these processes, as the surface deformation was captured in unusually high spatial and temporal resolution by satellite radar. 

In our study, we combine Interferometric Synthetic Aperture Radar (InSAR) data from the COSMO-SkyMed satellite, high resolution Digital Elevation Model (DEM), with a catalogue of >150 relocated moderated-sized earthquakes (M4.5-6) to study the spatio-temporal evolution of seismic and aseismic fault slip linked to dyking in the NMER. We focus on an area ~15 km north of the tip of the dyke, where we find fault patches showing both repeated seismic and aseismic slip occurring in close proximity, associated with surface deformation of <13 cm in 3 months. We consider three possible mechanisms for the observed fault behaviour: (1) that this is normal mainshock-aftershock sequence on faults governed by rate-and-state friction, (2) that elastic stress perturbations from the ongoing dyke intrusions reloaded the fault patches, or (3) that elevated pore-fluid pressure caused transient reductions in effective normal stress on the faults. Using slip and stress modelling, we will test these hypotheses and quantify how much seismic/aseismic strain is accommodated by pre-existing and newly formed faults, as well as the relative contribution of seismic/aseismic strain to accommodating shallow crustal extension during the dyking episode.

These findings provide new constraints on fault mechanics and the interaction with magmatic processes in rifting environments, improving our understanding of dyke-induced seismicity and the evolving nature of faults with repeated earthquakes.