Spatial variation of the present-day strain-rate and stress regime, from mid-Atlantic triple junction through north Africa to Aqaba transform zone

Résumé

The northern boundary of the African plate is one of the most complex and segmented plate boundary systems worldwide, extending from the Azores Triple Junction in the Mid-Atlantic Ocean to the Gulf of Aqaba in the eastern Mediterranean. This study investigates present-day kinematics by quantifying the seismic component of crustal deformation and its relationship with the regional stress field through the combined application of seismic moment tensor summation and stress tensor inversion. A newly compiled catalogue of 784 earthquakes (Mw ≥ 4.0), recorded between 1931 and 2025, was subdivided into 17 seismogenic zones covering the principal tectonic domains of the Africa–Eurasia and Africa–Arabia plate boundaries. Seismic moment tensor summation was used to estimate seismic deformation rates and zone-averaged seismic displacement vectors, whereas stress tensor inversion constrained the orientations of the principal stress axes and the prevailing tectonic regimes. Independent GNSS (GPS) and InSAR observations were used to evaluate the consistency of the inferred regional kinematic framework. The results reveal marked spatial variations in both seismic deformation rates and tectonic style, with a west-to-east transition from extensional regimes near the Mid-Atlantic Ridge to strike-slip deformation along the Gloria Fault and the Dead Sea Transform, and compressional to transpressional regimes across the Maghreb. Although most regions exhibit relatively low seismic deformation rates (<1 mm/yr), localized concentrations of seismic strain occur in the Gulf of Cadiz, northern Algeria, and the Gulf of Aqaba. The progressive rotation of the seismic displacement vectors closely matches the first-order regional kinematic pattern derived from independent geodetic observations. The strong agreement between seismic moment tensor summation, stress tensor inversion, and geodetic data supports the proposed tectonic framework. Rather than estimating plate velocities directly, the methodology provides robust quantitative constraints on the seismic component of crustal deformation, the segmentation of the Africa–Eurasia–Arabia plate boundary, and the tectonic processes governing regional seismic hazard.

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