Abstract
The wide variety of observed upper plate deformation styles, slab dips, seismic coupling, and other first order characteristics of convergent plate margins may be understood in terms of the motions of trenches ("rollback") and overriding plates ("retreat") relative to the mantle. However, due to convection, it is unlikely that an intrinsic or unique mantle fixed reference frame exists, hampering a global resolution of the relative importance of these processes. Active tectonics in the central Mediterranean region may provide an exceptional opportunity to investigate this issue. New high-precision GPS measurements of crustal velocity from a very dense network of stations within this plate boundary zone are revealing a complex pattern of present-day deformation that is not everywhere simply related to convergence of the major bounding plates, namely Nubia and Eurasia. In particular, GPS velocities representing the margins of the Adriatic Sea show present-day crustal velocities relative to stable Eurasia that are systematically oriented toward the northeast, at high angle to northwest-directed Nubia-Eurasia relative plate motion.