GPS Measurements of Plate Interactions and Intra-Plate Deformation in the Western Mediterranean

Massachusetts Institute Of Technology, Cambridge MA

Investigators

Abstract

For the past three years, MIT, Cornell University, and their Moroccan partners have developed and observed a network comprising 3 continuous (CGPS) and 22 survey-mode (SGPS) GPS sites in Morocco to determine more precisely Africa plate motion, the interaction of the African and Eurasian plates in the western Mediterranean, and deformation associated with present-day tectonics of the NW part of the African plate (Morocco). This work is being facilitated by complementary GPS studies being pursued by the PI's partners in Spain and Portugal with whom they are collaborating within the framework of the AMIGO Project (Atlantic and Mediterranean Interdisciplinary GPS Observations). Their work in Morocco is providing new kinematic information on plate motions and interactions that promise to constrain dynamic models for continental collision processes as well as intra-plate deformation. In this proposal, they request support to continue to monitor the Morocco GPS network for an additional 3 years, and to densify station coverage to determine better strain patterns in the most actively deforming regions. Preliminary GPS site velocities derived from three surveys over a 2 year period (10/99 - 10/01) have been resolved to ~2 mm/yr (1 sigma, or 5 mm/yr 95%). These uncertainties are on the order of the entire Africa-Eurasia convergence rate (~4 - 5 mm/yr in Morocco), and are not yet sufficient to provide reliable constraints on Africa plate motion or intra- plate deformation. However, the present velocity field does indicate overall WNW motion relative to Eurasia at about 6 +or- 2 mm/yr (1 sigma) for sites located south of the Rif Mountains, consistent within uncertainties with our new GPS estimates of Africa plate motion derived from available GPS data for the entire African plate (~ 4.7 mm/yr WNW). In contrast, sites located along the western Rif Mountains in NW Morocco indicate significantly slower northward motion, and possibly southward motion, suggesting present-day extension in the Alboran Sea. These two observations are consistent with the continuing NW motion of the African plate, active extension of the Alboran Sea (westernmost part of the Mediterranean between Morocco and Spain), and left-lateral, strike slip deformation between the western and eastern Rif. This overall, first-order pattern is consistent with deformation as estimated from earthquakes and neotectonic field studies. The PI's request continued support for 3 years to: 1) resolve better velocities on existing SGPS sites with surveys in 2002, 2003, 2004, and 2005 (all field costs borne by the Morocco side), and integrate the Morocco velocity field with GPS observations from Iberia, 2) establish 10 new SGPS sites in the Rif Mountains to constrain better apparent intra- late deformation (shortening and left lateral, strike-slip), 3) develop and apply elastic block, and finite element models for active deformation in the western Mediterranean, and, 4) further develop Moroccan in-country capabilities in GPS-geodynamic applications. This last task will allow the Moroccan partners (retaining the equipment provided by our joint project) to carry out all future GPS observations on their own and with Moroccan support beyond the requested grant period. We expect that future requests for support from NSF for this work, if required, will be restricted to data integration, modeling, and interpretation.