Rick Bennett obtained his PhD in the field of Geophysics in 1996 at Massachusetts Institute of Technology, after which he was employed as a Research Geodesist at the Harvard-Smithsonian Center for Astrophysics for 9 years.  He is currently an assistant professor in the Department of Geosciences at The University of Arizona.  His primary research interest is the application of space geodetic techniques to problems in active and neo-tectonics, and natural hazards. Modern space geodetic techniques allow for precise, quantitative determination of contemporary tectonic plate motions, the distribution of deformation within diffuse plate boundary zones, fault slip rates, earthquake slip distributions, isostatic adjustments to surface or sub-surface loads (e.g., glacial retreat), and other geophysical parameters.   These parameters are of basic importance to science and society, providing unique constraints on models for earthquake mechanics (e.g., source mechanisms, recurrence), lithospheric dynamics (e.g., mountain building), natural hazards (e.g., sea level rise, volcanoes and earthquakes), and similar phenomena associated with Earth’s surface deformation.

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 retrograde motions of trenches ("rollback"; Molnar and Atwater, 1978) and overriding plates ("retreat"; Chase, 1978) relative to the mantle.  However, convective flow makes it 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 provides an exceptional opportunity to investigate this issue.  The geologic evolution of the central Mediterranean is frequently attributed to the subduction and rollback of the leading edge of the Nubia plate beneath Eurasia.  According to this predominant viewpoint, the coupled late Cenozoic evolution of the Tyrrhenian back-arc basin and Apennines arc system was controlled primarily by the negative buoyancy of a slab of oceanic or highly attenuated continental Mesozoic lithosphere.  However, the present-day kinematics of the Nubia-Eurasia plate boundary zone is difficult to reconcile with ongoing slab rollback, leading some to the conclusion of recent or ongoing Apennines slab detachment, possibly associated with the introduction of the buoyant Adria passive margin to the Apennines trench.  Yet, Neogene slab rollback followed by Quaternary detachment fails to address why present-day motion of Adria, kinematically distinct from both Eurasia and Nubia, continues to work against the resistive strength of the crust and lithosphere.  In this talk, I will present new GPS velocity results for ~1000 CGPS stations, with dense sampling in the central Mediterranean region.  These data form the basis for an investigation of circum-Adria kinematics relative to plate fixed and mantle-fixed (e.g., hotspot and other) frames of reference. I will explore an alternative model for the late Cenozoic evolution of the central Mediterranean region consistent with the pattern of modern plate boundary zone deformation, involving the entrainment of Adria slabs in a regional-scale upper mantle counter flow between thick, converging, continental Eurasia and Nubia lithospheres.