Present-day deformation of the French northwestern Alps/southern Jura mountains: comparison between historical triangulations

The change of the coordinates of 44 geodetic points between two surveys, epochs 1930–36 and 1979–84 are studied. The discussion is supported by strain rate tensors and angular shear rates for different sets of three adjacent points as well as by calculated displacements together with their confidence ellipses. The southern Jura mountains may undergo a relatively homogenous pattern of deformation characterized by a roughly east—west to NE—SW compression and by a significant westward motion (5 mm yr−1) relative to the frontal Jura mountains. This deformation would be compatible with the few focal mechanisms of earthquakes available for this area. A displacement of nearly 2 cm yr−1 affected a geodetic point north of Annecy. Unfortunately, this point is the only one that shows such a movement, we cannot exclude a local displacement of this benchmark.