Crustal strain in the Southern Alps, France, 1948-1998

Active tectonics in the Western Alps is revealed by a moderate level of sei smic activity and geological evidences for Quaternary deformation. We prese nt new geodetic determinations of the current strain rates in the southern part of the Western Alps, that complement existing results in Provence, the Jura, and the Subalpine and Belledone massifs around Grenoble. We combined first- and second-order triangulation data collected in 1948 with global p ositioning system (GPS) data collected in 1998. We estimate shear strain ra tes of 0.1-0.2 mu rad yr(-1) over distances on the order of 30 km, signific antly different from zero in most of the network. We obtain NW-SE to N-S co mpressive shear strain directions over most of the area, in agreement with the seismological and geological data. These geodetic estimates correspond to long-term overall N-S to NW-SE shortening of 2-4 mm yr(-1) over the stud y area, on the same order as the far-field shortening measured by continuou s GPS on the Grasse-Torino baseline (-2.0+/-0.5 mm yr(-1)), that incorporat es our geodetic network. These results provide new constraints on interseis mic strain in the Western Alps. (C) 2000 Elsevier Science B.V. All rights r eserved.