PRESENT-DAY DEFORMATION OF THE DAUPHINE ALPINE AND SUB-ALPINE MASSIFS(SE FRANCE)

The positions of 20 geodetic points surveyed in 1946-1952 by the Insti tut Geographique National in the Grenoble area (western Alps) were rem easured in 1993-1994 using GPS. We evaluate the displacements of the c ommon points of the networks between the two surveys, and calculate th e strain-rate tensors for different sets of three adjacent points. The significant N70 degrees shortening direction observed at the boundary of the Belledonne and Taillefer massifs suggests that the dextral str ike-slip motion between the External Crystalline Massifs (ECM) and the Subalpine domain is still active, Geological evidence suggests that t his deformation, which is compatible with the few focal mechanisms ava ilable for the area, occurred throughout the late Neogene, Our data al so suggest a roughly 3-5 mm yr(-1) active shortening concentrated at t he external front of the Subalpine chains, This thrust motion results in a principal axis of compression orientated N130 degrees, oblique to the direction of shortening observed in the ECM. This change in direc tion is also seen in in situ stress measurements, This motion may mark the southward continuation of the active fault observed in the Jura m ountains by Jouanne, Menard & Darmendrail (1995).