Unlocking the Hidden Forces: Deformation and associated Stress Distribution in the present-day Geneva Basin and Jura Fold-and- Thrust Belt

In foreland fold-and-thrust belts, the distribution of deformation and of the associated stress field can notably be perturbated due to local-scale features such as tectonic structures or surface topography. In the frame of geothermal exploration in the Geneva Basin, constraining possible future deformation in the area and the associated state of stress is of particular interest. If current seismicity indicates that the Geneva Basin is tectonically active, few data regarding the state of stress in the area are currently available. The goal of this study is to understand under which conditions deformation could localise in the study area, by using numerical modelling. In a first regional part of the study, we investigate the impact of the friction along the basal décollement on the deformation and on the stress field along a 2D section. Knowing the weak décollement property in the area, results indicate that future deformation is more likely to localise in the Geneva Basin or at the frontal part of the Jura fold-and-thrust belt. Localisation of deformation depends more on surface topography rather than on décollement geometry. The décollement geometry influences the presence of stress concentrations, which could lead to weakness zones within the section. In the second part of the study, we used a simplified prototype section based on interpretation of a seismic survey in the Geneva Basin. The impact of friction along the inherited faults on incipient deformation was investigated. Results indicate that existing faults can be reactivated by decreasing their friction angle. In the Geneva Basin, the Humilly Fault is the less likely to be reactivated, due to its orientation, compared to the Reculet and Salève thrusts. The distance to criticality is thus strongly determined by the internal structure of the considered prototype, the frictional properties, and orientations of the existing faults. In the case where deformation localises in the Geneva Basin, the differential stress distribution depends on the décollement friction and geometry, and of the friction along the existing faults.