Lithosphere-asthenosphere interaction as the source for intraplate deformation in the Gulf of Guinea

Despite extensive research, intraplate earthquakes and required intraplate deformation remain relatively unexplained. To explore this problematic, we tested the possibility that these could derive from the dynamic interaction between the lithosphere and the upper mantle. This was performed by conducting a thorough geophysical exploration of a region with both low plate velocities and clear asthenosphere dynamics, specifically the Gulf of Guinea (GOG) and adjacent Western Africa.

In this work, we developed 3D numerical geodynamic models of the asthenosphere-lithosphere interaction in the GOG, ran with the state-of-the-art LaMEM modelling code. To assess the contribution of individual intraplate deformation sources, we tested various initial/boundary conditions namely: (a) the spreading rate of the individual segments of Central Atlantic mid-ocean ridge, (b) the presence/absence of weak zones, such as the Romanche or Central-African shear zones, as well as (c) the stress contribution by an active mantle plume head with varying width. Seismicity data was utilized as a criterion to assess the validity of the modelled stress/strain localization sites.

Our results suggest that intraplate deformation within the GOG is mostly controlled by the spreading rate of the mid-ocean ridge, with different localization sites deriving from their relative proximity to the shear zones and plume head. This work aims to expand our knowledge of intraplate deformation mechanisms and to contribute towards improving seismic hazard assessment away from plate boundaries.

This work was supported by the European Union and the Instituto Dom Luiz (IDL) Project under Grant UIDB/50019/2020, and it uses computational resources provided by C4G (Collaboratory for Geosciences) (Ref. PINFRA/22151/2016). It was also partly supported by the Fundação para a Ciência e a Tecnologia (FCT) in the content of the Project SHAZAM “Sismicidade e Perigosidade da Margem Atlântica sub-Saariana,” with the reference PTDC/CTA/GEO/31475/2017; POCI-01-0145-FEDER-031475, co-financed by FEDER-COMPETE/POCI 2020.