Relative contribution of the Hellenic slab rollback and movement of the North Anatolian Fault to the deformation in western Anatolia

Abstract The Anatolian-Aegean region, located at the convergence of the Eurasian, African, and Arabian plates, is one of the most tectonically active deformation zones on Earth that is primarily been controlled by the African slab rollback beneath the Hellenic-Cyprus Subduction Zone (HCSZ) and the movement of the North Anatolian Fault Zone (NAFZ). The Mw7.0 2020 Samos earthquake, for instance, is an expression of the N-S directed extensional tectonic regime developed in response to the African slab rollback. This study quantitatively evaluates the respective contributions of the NAFZ kinematics and the rollback of the subducting African slab along the HCSZ to the present-day deformation of the Anatolian–Aegean domain to better elucidate the tectonic development and its potential seismic hazard in this region. Using a two-layer elastic-viscoelastic Earth model and GPS velocity data, we decomposed the observed velocity field into the rotational motion of the Anatolian-Aegean system and the residual effects associated with slab rollback. The Anatolian-Aegean region is enclosed by the circuit of the NAFZ, the East Anatolian Fault Zone, and the HCSZ. We assigned slip rates over the circuit according to the rotation pole located off Egypt and estimated the velocities at each GPS station with varied angular velocities. We performed a series of forward and inverse calculations to determine the optimal slip rates along the NAFZ and HCSZ that minimize the misfit between the estimated and observed velocities. Our results indicate an optimal right-lateral slip rate of ~31 mm/yr along the NAFZ, which is consistent with the sum of the observed slip rates along the northern and southern strands of the NAFZ, as well as an average slip rate of ~50 mm/yr for the HCSZ, peaking around western and eastern Crete. These findings confirm that the westward extrusion of Anatolia is predominantly driven by the NAFZ slip, while the southwestward motion and N-S extension across the Aegean Sea are governed by Hellenic slab rollback. The stress accumulation rates derived from the optimum model demonstrate strong consistency with regional focal mechanism solutions, reproducing strike-slip stress patterns across central Anatolia and extensional stresses within the Aegean domain.