Numerical modelling of lithosphere-asthenosphere interaction and intraplate deformation in the Gulf of Guinea

Despite extensive research, intraplate deformation and associated earthquakes remain elusive. We argue that one potential reason for its occurrence is the interplay between the lithosphere and the upper mantle dynamic processes, specifically the lithosphere-asthenosphere interaction. To explore this possibility, we targeted the Gulf of Guinea and adjacent Western Africa, a region with low plate velocities and clear asthenosphere dynamics, which allows for the isolation of the underlying dynamic constraints which govern intraplate deformation. An in-depth understanding of intraplate deformation mechanisms will contribute towards the improvement of seismic hazard assessment away from plate boundaries. Thus, here we present exploratory 3D numerical geodynamic models of the asthenosphere-lithosphere interaction in the Gulf of Guinea, ran with the state-of-the-art modelling code LaMEM. We employ different initial/boundary conditions such as: (a) different spreading rates for the Atlantic mid-ocean ridge (from 5 to 25 mm/yr), (b) rheological/lithological configurations (accounting for the cratonic/mobile nature of the region), (c) the presence/absence of weak zones (e.g., the Romanche/Central-African shear zones), and (d) the effect exerted by an active mantle plume. Seismicity data was employed to rank the models to ensure the validity of our results. Preliminary results suggest that intraplate deformation within the Gulf of Guinea is influenced by the spreading rate of mid-ocean ridge, with stress being localized around the ocean-continent transition and existing shear zones. This work was developed in the frame of SHAZAM (POCI-01-0415-FEDER-031475). FCT is further acknowledged for support through project UIDB/50019/2020-IDL.