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 perturbed due to local-scale features such as tectonic structures or surface topography. In the context of geothermal exploration and the planning of the future circular collider (CERN) in the Geneva Basin, it is of particular interest to constrain possible future deformation in the area and the associated stress state. 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 based on Limit Analysis. In a first regional part of the study, we investigate the impact of the basal décollement strength 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. Location of deformation in the Geneva Basin 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 surveys in the Geneva Basin. The impact of the inherited faults strength 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 failure potential 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 strength and geometry, and of the strength of the existing faults.