Strike-slip fault zone architecture in folded Upper Malm limestones at Gorges de l’Orbe, Central Internal Jura, Switzerland

Strike-slip fault zones often play a key role in controlling brittle deformation patterns in fold-and-thrust belts. Yet, the distribution of associated fractures and their interactions with fold-related structures remain insufficiently understood across scales and as part of the deformation history. In the Jura Mountains, previous work in the Central Internal Jura, notably at Creux-du-Van, proposed a multi-scale hierarchy of strike-slip faults and associated fracture networks based on sub-seismic structures spanning meter- to kilometer-scale. This study extends the multi-scale structural analysis to a regionally mappable ~12 km long N–S striking sinistral fault zone, the Suchet Fault. The fault is exposed along the E–W-oriented Gorges de l’Orbe, where incision into Upper Malm limestones enables largely continuous outcrop-scale access to fault-related damage zones.

To address the multi-scale character of this system, we combine field-based structural mapping at 1:5,000 scale and three-dimensional structural interpretation of publicly available aerial LiDAR data (SwissALTI3D) with systematic fracture data acquisition along four scanlines totaling 157 m. Scanlines are positioned at varying distances from the fault core, defined by the presence of fault breccia and gouge lenses, and across western and eastern structural compartments, spanning fault-proximal to fault-distal domains. This configuration enables comparison between fracture populations associated with fault-zone architecture and those interpreted as fold-related or background fracturing.

The Suchet Fault separates two contrasting structural domains. The western compartment is characterized by NW–SE striking fold trains, whereas the eastern compartment exhibits a comparatively flatter structural geometry. Within the vicinity of the fault trace, bedding orientations rotate progressively toward the N–S fault trend, with gentle eastward dips (~15°). Locally, near the fault core, bedding dips steepen and may reach up to 70°, indicating increased strain localization within the damage zone. LiDAR-based structural interpretation identifies three dominant fracture populations, with the NW–SE striking set displaying comparatively longer fractures than the N–S and NE–SW sets.

Fault-slip indicators show dominant subvertical conjugate strike-slip pairs at outcrop scale, comprising sinistral N–S to NNE-SSW striking faults and dextral NW–SE striking faults. Preliminary paleostress inversion analysis indicates a strike-slip regime characterized by a subhorizontal NW-directed maximum principal stress and a subvertical intermediate stress, consistent with results from other sectors of the Central Internal Jura. Fracture density (P10) increases toward the fault core, with values close to the brecciated core notably higher than those measured beyond 100 m.

This study emphasizes the need for robust fracture set definition and sequencing as a basis for structural analysis, including paleostress orientations and spatial variations in fracture intensity and anisotropy. This study evaluates whether structural patterns and paleostress behaviors identified at Creux-du-Van are comparable to those observed in the Gorges de l’Orbe area, at the scale of larger strike-slip fault zones. It also considers the potential regional implications of these structural features for fracture-controlled fluid flow in the Jura Mountains and potentially downstream, in the geothermal reservoirs beneath the Molasse Basin.