THE STRAIN-RATE FIELD IN THE EASTERN MEDITERRANEAN REGION, ESTIMATED BY REPEATED GPS MEASUREMENTS

We use the combined GPS velocity field of the eastern Mediterranean fo r the period 1988 to 1996 to determine crustal deformation strain rate s in a region comprising the Hellenic are, the Aegean Sea, and western Anatolia. We interpret the velocity field and determine the strain ra te tensor by the spatial derivatives of the collocated motion vectors. The region following the line Marmara Sea, North Aegean Trough, north ern central Greece, and the central Ionian islands is associated with strong right-lateral shear motion, with maximum shear strain rates of 180 nano-strain/a (180 x 10(-9)/a). In the central Aegean Sea, N-S-ori ented extensional processes prevail, reaching 100 nano-strain/a. The s outhern Aegean is characterized by relatively small strain rates. Maxi mum extensional components of the strain rate tensor, reaching 150 nan o-strain/a in a N-S direction, are found in central Greece. The Hellen ic are is associated with moderate are-parallel extension and strong c ompression perpendicular to it. Projections of the strain rates parall el to the major fault zones reveal that the northern Aegean is governe d by the westward continuation of the North Anatolian Fault Zone which is associated with strong dextral shearing (maximum 220 nano-strain/a ), accompanied by numerous large earthquakes in this century. (C) 1998 Elsevier Science B.V. All rights reserved.