Post seismic relaxation processes in the Aegean-Anatolian system: insights from space geodetic data (GPS)and geological/geophysical evidence

Variation of motion rates and stress redistribution in the Anatolian-Aegean region induced by the last sequence of strong earthquakes occurring along the North Anatolian fault system since 1939 are investigated by a 2D numerical approach. The model is constituted by an elastic lithosphere coupled with a viscous asthenosphere. The predicted perturbations of the velocity field may account for the major features of the present day kinematic pattern in the study area, inferred from space geodetic data (GPS). This result can provide a possible explanation for the considerable difference between the long term average motion rates (5-10 mm/y), deduced by fault offset measurements along the North Anatolian fault and by the seismic history of this fault, and the geodetic velocities (20-30 mm/y) in the Anatolian-Aegean system. Furthermore, the slow migration of the velocity perturbations in the lithosphere, controlled by the coupling with the viscous asthenosphere, can explain the fact that the present day average velocity in the Aegean area (32 mm/y) is higher than those observed in western (24 mm/y) and eastern Anatolia (18 mm/y). The computed post seismic strain energy rate redistribution can also account for the time pattern of the seismicity rate in the study area during the last 60 years. The results obtained in this work might also have implications for the understanding of the geodynamic setting in the Mediterranean area, in that they indicate that the higher motion rates observed in the Aegean region with respect to those in Anatolia must not necessarily be interpreted as an effect of a slab pull mechanism in the Hellenic trench.