Long-lasting transcurrent tectonics in SW Alps evidenced by Neogene to present-day stress fields

The SW Alps are an active orogen undergoing intra-mountainous extension and peripheral compression. We discuss the significance of syn-orogenic extension based on a comparison of paleo-stress derived from fault-slip data inversion reflecting the long-term (<12 Ma) evolution of SW Alps and the present-day stress state obtained by the inversion of the focal mechanisms of the last 30-years seismicity. The resulting stress states of long-term and active tectonic regimes are in good agreement, showing that extension accompanies strike-slip and reverse faulting in the southern part of the belt. The extensional deformation regime is limited to specific tectonic domains that can be interpreted as 'transitional' between pure strike-slip segments where the deformation concentrates on inherited ductile shear zones that were formed between 32 degrees and 20 Ma ago. We thus propose that the extensional deformation in the SW Alps can be defined as a local deformation in a pull-apart type domain (High Durance - Jausiers area) or above slowly exhuming internal massifs (Dora Maira - Ivrea Body) along a curved boundary between the slowly rotating Apulian block and the relatively immobile Western Europe. The transcurrent fault system merges into a compressional front along the Mediterranean - Ligurian coast mainly to the east of San Remo. (C) 2014 Elsevier B.V. All rights reserved.