Velocity Field of the Aegean-Anatolian Region from 3D Finite Element Models

Abstract.

In order to investigate the geodynamic processes and rheological parameters, which are principally responsible for the observed surface deformation, a three-dimensional finite element model of the Eastern Mediterranean was built up. The northward movement of the Arabian and the African plate relative to the Eurasian plate has been assumed to control the tectonic evolution of the Aegean-Anatolian block since the Miocene. The indentation of Arabia forces the Anatolian region to escape westwards along the North and the East Anatolian fault, whilst the Aegean region is extended by southward retreat of the Hellenic arc subduction zone. Major faults were modelled as contact surfaces with Coulomb friction. Boundary conditions imposed were the slab pull beneath the Hellenic arc and the northward movement of the African and the Arabian plate using a rigid plate model. An elasto-visco-plastic rheology was applied for the modeling time of 0.5 Ma. By varying the properties a set of parameters was determined which gives a minimal mean deviation between the modeled velocity field and GPS data from 45 observation sites. This comparison is considered justified, since even though the geodetic observations are representing a short time period, the geodetically derived displacement rates coincide with long-term rates derived from seismicity and fault-slip data. The best-fitting model was attained with the following parameters: (a) friction coefficient between 0.2 and 0.45 along the subduction zones and the main faults, (b) slab pull stresses of 150 MPa, (c) cohesive strength of 460 MPa in Anatolia (compressional regime) and (d) cohesive strength of 40 MPa in the Aegean (extensional regime). In this case the mean deviation was 21% in magnitude and $\pm 10^{\circ}$ in azimuth. The strain rate field of the model has a minimum in the Anatolian region ($< 2\cdot 10^{-15} {\rm s}^{-1}$) and a maximum in the Aegean region (5-10 $\cdot$ 10-15 s^-1). These values are comparable with the strain rates derived from seismicity. The velocity field of the best-fitting model shows almost rigid westward movement of Anatolia and SSW oriented extension in the Aegean region.