PRESENT-DAY DYNAMICS OF THE AEGEAN REGION - A MODEL ANALYSIS OF THE HORIZONTAL PATTERN OF STRESS AND DEFORMATION

In order to gain quantitative insight into the forces that control the present-day stress field and pattern of horizontal motions in the Aeg ean region, we adopt a forward model approach. Mechanisms that have be en proposed to explain the present-day tectonics are represented, to f irst approximation, in terms of the expected force distributions. On t he basis of a thin elastic shell representation of the Aegean lithosph ere we then calculate the stress field and displacements associated wi th these force sets and compare the results with observations of the s tate of stress based on geological studies of fault kinematics, strain as expressed by earthquake focal mechanisms, and horizontal motions m easured by means of satellite geodesy. The two most commonly cited mec hanisms suggested to control the Aegean tectonics, (1) the push exerte d by the westward moving Anatolian block and (2) forces associated wit h the Hellenic subduction zone, are first analyzed separately. It is f ound that the westward Anatolian push alone does not explain the obser ved prevalence of tensional stress. This is also expressed in a mismat ch between the displacements computed to result from the westward push and the observed horizontal velocities. Regarding the forces on the A egean overriding margin, we find that a model with outward pulling for ces of uniform magnitude, acting normal to the arc from the SW Pelopon nese to Rhodes, yields a stress field that matches the observed patter n of tension to a large extent. This distribution of forces is consist ent with the notion of gravitational spreading of the Aegean lithosphe re. The pattern of seismic strain of the overriding margin may evidenc e the occurrence of a small additional resistive force. Although the p revalence of tension thus appears due mainly to the subduction-related forces, other aspects of the stress field and also the pattern of hor izontal motions indicate that these forces act in combination with wes tward push. Our model results allow us to address the relation between the forces experienced by the upper plate and the kinematics of subdu ction, not just in terms of a vertical cross section but also by takin g into account the along-arc dimension.