Fig. 2

Regional geological map of the Western Internal Jura, projected in the CH1903 + LV95 coordinates system. A succession of major, large-scale folds and ramp-flat thrusts, as well as major strike-slip faults can be recognized in the study area. Orientation of the strike-slip faults, thrusts and fold axial traces between the Vuache Fault and St-Cergue-Morez Faults are summarized in the rose diagram. The ramp-flat thrusts and the axial fold traces are oriented SSW-NNE. The strike-slip faults form a conjugate system with NNW-SSE sinistral faults and WNW-ESE dextral faults. Major dextral faults are less developed in the study area but the dextral offset is accommodated by smaller and numerous strike-slip faults forming strike-slip corridors. Oblique ramps are common in this area, per example, between the Crêt Chalam Thrust and the Vuache-Forens-Les Bouchoux (VFB) Fault. The VFB Fault and a curved Léaz-Sandézanne Axis define together a triangular zone in map view (the Léaz-Champfromier Relais) bounded in the north by the Monnetier Backthrust. The localization of the detailed geological map (Fig. 5) and the trace of the initial and final cross-sections (Figs. 7, 11) are represented by the black square and the black line. The sections cross 5 five major thrusts, from SE to NW, the Reculet Thrust, the Crêt Chalam Thrust, the Tacon Thrust and the Bienne Thrust. The section ends at the front of the Oyonnax Backthrust, which is considered to be the boundary between the Internal Jura and the External Jura (Wildi & Huggenberger, 1993). F. Strike-slip Fault, T. Thrust, A. Anticline, S. Syncline, VFB Vuache-Forens-Les Bouchoux Fault