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 Europe as shown by continuous GPS measurements and the low level of Alpine seismicity both indicate that present-day deformation in the western Alps is very moderate, Nevertheless, from historical seismicity records, the Moyenne Durance Fault can be identified as an active structure, and a brief neotectonic and geomorphological analysis indicates that Plio-Quaternary deformation occurred in the northern Valensole Basin and in the Digne Nappe. A comparison is made between 1949 and 1952 triangulation data and 1997 GPS data to estimate the current deformation in the Digne Nappe and around the Moyenne Durance Fault in the southwestern Alps. The deformation is represented by the maximum angular shear rates needed to make the characterization of the deformation independent of the rigid rotation and scale effects that are introduced in the velocity field when using triangulation data, Errors on maximum angular shear rates are simulated using a Monte Carlo analysis of the errors of the triangulation data. The main results are: (1) the existence of moderate deformation in the inner part of the Digne Nappe; (2) deformation of the northern Valensole Basin; (3) significant deformation in the southern part of the Moyenne Durance Fault; and (4) a lack of measurable deformation in the southern Valensole Basin-Provencale range area and south of the Lure Mountain.