Numerical modelling of the Aegean-Anatolian region: geodynamical constraints from observed rheological heterogeneities

High strain rates and intense seismic activity characterize both the bounda ries and the interior of the Aegean-Anatolian plate: the availability of ge odetic and geophysical data makes this region ideal to make detailed models of continental deformation. Although the deformation occurring in the Aege an-Anatolian plate may be regarded as the primary effect of the Arabian ind enter push, it has already been demonstrated that this mechanism cannot acc ount for the observed extrusion/rotation of the whole plate. We investigate the present-day steady-state anelastic deformation of the Aegean-Anatolian plate by a thin plate thermomechanical finite element (FE) model that acco unts for realistic rheological mechanisms and lateral variations of lithosp heric properties. Studying the region with uniform models, where average va lues for thermal and geometric parameters are chosen, we find that two tect onic features, in addition to the Arabian plate push, are critical to repro duce a velocity field that gives a reasonable fit to the observations. The first is the E-W constraint of NW continental Greece, related to the collis ion between the Aegean-Anatolian plate and the Apulia-Adriatic platform, re quired in the model to attain the SW orientation of the velocity field alon g the Hellenic Are. The second is the trench suction force (TSF) due to sub duction of the African lithosphere, which is needed to fit the observed mea n extrusion velocity of 30 mm yr(-1) along the Hellenic Arc. Uniform models are useful to study the sensitivity to the interplay of rheological/therma l parameters in a simplified framework but, in all cases, predict a strong deformation localized along the Hellenic Arc, whereas geodetic and seismolo gical data show that the highest strain rates are located in western Anatol ia. Furthermore, uniform models are non-unique in the sense that since we m odel a vertically averaged thin plate, different thermal and rheological pa rameters can be combined to yield the same lithospheric strength. We accoun t for internal sources of deformation with heterogeneous models, where the available constraints on lateral variations of crustal thickness and surfac e heat flow have been included. The heterogeneous distribution of lithosphe ric strength contributes to ameliorate the fit to geodetic and stress data, since the predicted velocity field is characterized by an acceleration fro m E to W, with a sharp increase in the proximity of the western margin of t he Anatolian peninsula, where the highest rates of intraplate deformation a re observed. In our model this partitioning of the deformation is due to th e different rheology of the Aegean Sea, which, being slightly deformable, t ransmits the TSF to the western margin of Anatolia. Our results are consist ent with the interpretation of the Aegean-Anatolian system as a single, rhe ologically heterogeneous plate.