The GPS velocity field of the Aegean. New observations, contribution of the earthquakes, crustal blocks model

Abstract

SUMMARY We calculate and analyse the coordinate time-series of 282 permanent GPS stations located in Greece and 47 in surrounding countries. The studied period is 2000–2020. The average GPS time-series length is 6.5 yr. The formal velocity uncertainties are rescaled to be consistent with the velocity scatters measured at 110 pairs of stations separated by less 15 km. We remove the effect of the crustal earthquakes of Mw ≥ 5.3. We quantify and model the post-seismic deformations. Two relaxation times are usually needed: one short of some weeks and one long of 1 yr or more. For the large Mw = 6.9 events of Samothraki 2014 and Methoni 2008, the post-seismic deformation equals or exceeds the coseismic one. We detect at three stations a deformation transient in May 2018 that may correspond to a slow earthquake beneath Zakynthos and northwest Peloponnese, with equivalent magnitude 5.8. The density and accuracy of the velocities make it possible to better quantify several characteristics of the deformation in the Aegean, in particular: (i) the transition from the Anatolian domain, located in the southeast, to the European domain through the western end of the North Anatolian fault; (ii) the north–south extension in the western Aegean; (iii) the east–west extension of the western Peloponnese; (iv) the clockwise rotation of the Pindos; (v) the north–south extension in central Macedonia. Large parts of the central Aegean, eastern Peloponnese and western Crete form a wide stable domain with internal deformation below 2 nstrain yr−1. We build a kinematic model comprising 10 crustal blocks corresponding to areas where the velocities present homogeneous gradients. The blocks boundaries are set to fit with known localized deformation zones, for example, the rift of Corinth, the North Anatolian fault and the Katouna fault. When the velocity steps are clear but not localized, for example, through the Peloponnese, the boundary line is arbitrary and represents the transition zone. The model fits the velocities with a root-mean-square deviation of ±0.9 mm yr−1. At the boundaries between blocks we compare the predicted and observed deformations. We find shear rates of 7.4 and 9.0 mm yr−1 along the Movri and Katouna faults, 14.9 and 8.7 mm yr−1 along the North Anatolian fault near Lemnos and near Skopelos respectively, extension of 7.6, 1.5 and 12.6 mm yr−1 across the Gulf of Patras, the Trichonis Lake and the Ambracian Gulf. The compression across western Epirus is 3.7 mm yr−1. There is a dextral transtensional movement of 4.5 mm yr−1 between the Amorgos and Astypalea islands. Only the Ionian Islands region shows evidence of coupling along the subduction interface.