Surface velocity field of the Ibero-Maghrebian segment of the Eurasia-Nubia plate boundary

Abstract

SUMMARY We process continuous GPS data distributed over the Iberian Peninsula, complemented by a few stations in France and North Africa, to constrain the displacement field in the surrounding area. A surface velocity field is derived from the time-series of daily solutions for each station, whose observations span 3.5 yr or longer. We find that most of Iberia forms a stable block fixed relative to Eurasia in which residuals have a weighted rms value of 0.85 mm yr−1 and are all below the computed accuracy for each station. Stations in northern Morocco exhibit a motion close to what would be expected for stable Nubia, in which residuals have a weighted rms value of 0.70 mm yr−1 and are also all below computed accuracies. The most distinctive behaviour is found at stations along the southern coast of Spain and the northern coast of Morocco, where larger and more westward velocities are found. Three stations in southern Iberia show differences with respect to stable Eurasia that can reach 4.4 mm yr−1 and are distinctly larger than computed accuracies. We hypothesize that this peculiar behaviour is not only a consequence of the Nubian–Eurasian plate convergence, but also a result of a local lithospheric process, particularly the effect of the Gibraltar slab, as previously suggested by seismic tomography and geological modelling.