Current deformation of the Digne Nappe (southwestern Alps) from a comparison between triangulation and GPS data

The negligible present-day convergence between northern Italy and stable Eu rope as shown by continuous GPS measurements and the low level of Alpine se ismicity both indicate that present-day deformation in the western Alps is very moderate, Nevertheless, from historical seismicity records, the Moyenn e Durance Fault can be identified as an active structure, and a brief neote ctonic and geomorphological analysis indicates that Plio-Quaternary deforma tion occurred in the northern Valensole Basin and in the Digne Nappe. A com parison is made between 1949 and 1952 triangulation data and 1997 GPS data to estimate the current deformation in the Digne Nappe and around the Moyen ne Durance Fault in the southwestern Alps. The deformation is represented b y the maximum angular shear rates needed to make the characterization of th e deformation independent of the rigid rotation and scale effects that are introduced in the velocity field when using triangulation data, Errors on m aximum angular shear rates are simulated using a Monte Carlo analysis of th e errors of the triangulation data. The main results are: (1) the existence of moderate deformation in the inner part of the Digne Nappe; (2) deformat ion of the northern Valensole Basin; (3) significant deformation in the sou thern part of the Moyenne Durance Fault; and (4) a lack of measurable defor mation in the southern Valensole Basin-Provencale range area and south of t he Lure Mountain.