THE DYNAMICS OF DEFORMATION IN THE AEGEAN: CONSTRAINTS FROM A DENSE FIELD OF CRUSTAL VELOCITY

A new geodetic velocity field for Greece, the Aegean and Turkey, derived from about 450 survey-mode and continuous GPS sites is used to test kinematic and dynamic models for this classic area of continental deformation. We first show that kinematic models treating the lithosphere as a set of rigid or elastic blocks satisfy the data only when the blocks are so small as to be indistinguishable from a continuum. We then analyze the deformation of the region using a simple thin-viscous-sheet model, containing only two free parameters: the effective viscosity of the lithosphere and the normal traction across the Hellenic plate boundary. We show that the principal features of the deformation between eastern Turkey and the southern Aegean can be explained by variations in gravitational potential energy acting on the lithosphere of the region. The velocities of the 450 GPS sites are fit with an RMS misfit of ~3 mm/a, the calculated distribution of strain rates matches that observed, and the active faulting of the region agrees with that predicted from the calculated strain rates. The deformation of the region is driven almost entirely by contrasts in gravitational potential energy related to isostatically compensated contrasts in surface height; no additional traction is required at the Hellenic trench from “trench roll-back”. The low rates of deformation in Anatolia and South Aegean result not from their strength, but from the low level of deviatoric stress acting upon them.