A detailed study of the active crustal deformation in the Aegean and surrounding area

A detailed study of the active crustal deformation in the Aegean sea and surrounding area is presented. The estimation of the deformation velocities is not performed in broad seismic zones but in seismogenic sources of limited spatial extent, where the seismic energy is practically released, in order to describe the spatial variations of the components of the strain rate tenser. The deformation analysis is based on previous work where the seismicity and the available focal mechanisms are used separately for estimating the rate and shape of the deformation, respectively. The calculations were performed for 63 seismogenic sources identified in the Aegean sea and surrounding area which belong to eight belts with an almost uniform orientation of the stress field. Along the coasts of Albania and northwestern Greece (up to Leukada island) the collision of the Adria plate with Eurasia results in a compressional velocity of about 4 mm/yr in a direction (N49 degrees E) almost normal to the coast line. The dextral movement with almost 3 cm/yr along the Cephalonia transform fault with strike N45 degrees E is expressed as an almost equal extension and compression in N-S and E-W direction, respectively. Along the convex (outer) part of the Hellenic are a crustal shortening of 1.3 cm/yr is observed in a mean direction N34 degrees E. The direction of this shortening is almost constant from the southern Ionian islands (Zakynthos) up to Rodos while the shortening rate does not significantly change from the outer sources to the inner ones. The Aegean sea and surrounding area is characterised by an extensional deformation. The direction of the maximum extension in the northern part of this area shows an anticlockwise rotation from east to west. Thus, this extension has a NNE direction in northwestern Turkey (N11 degrees E), a NNW direction in central and northern Greece as well as along the southern Aegean volcanic are and its extension to southwestern Turkey (N12 degrees W) and a WNW direction in the westernmost part of this extensional area (N72 degrees W). The mean value of the extensional velocities in this area is 5 mm/yr. The northern part of Asia Minor and of the Aegean sea is characterised by the dextral strike-slip movement of about 2 cm/yr of the North Anatolian fault and its continuation in the northern Aegean, where this movement gradually decreases to about 6 mm/yr. The vertical crustal (upper 10 km of the crust) thickening is about 2 mm/yr along the convex side of the Hellenic are and the vertical crustal thinning is about 1 mm/yr in the Aegean sea. These values were obtained from the component U-33 of the velocity tenser.