Building a large-scale 3D geological model of the Swiss Alps: First results

From 2024 to 2030, the Swiss Geological Survey (swisstopo) leads the Swiss Alps 3D (SA3D) project as part of the swisstopo National Geological Model (NGM) program. The project brings together eight modelling and research teams from several universities with the objective to develop one coherent, large-scale 3D geological model of the Swiss Alps subsurface. The model targets the major structural and lithostratigraphic boundaries of the region and will serve as a regional geological reference framework for future high-resolution studies. It will support a wide range of applications, including infrastructure planning, groundwater management, georesource assessment, natural hazard analysis, as well as education and research.

This contribution presents results from the first two years of SA3D modelling in the Subalpine Molasse, Prealps, Helvetic, and Western Penninic tectonic domains, with emphasis on practical solutions developed to address key methodological challenges. The SA3D models are structured around four core components: (i) input datasets, (ii) 2D geological maps, (iii) reference cross-sections, and (iv) 3D meshes. Ensuring internal consistency among these elements, both at the surface and at depth, represents a primary challenge. This challenge is amplified by sparse subsurface data, limited seismic profiles and boreholes, the large extent of the study area, and the extreme structural complexity of the Alpine Orogen. These constraints limit the range of applicable modelling approaches (implicit versus explicit) and require rigorous integration of all components. Coordinating eight independent projects to produce a unified, technically and conceptually consistent model demands close collaboration and methodological harmonization across the different modelling teams.

By addressing these challenges, SA3D provides unprecedented insight into the largely unexplored Alpine subsurface. Reconstruction of the three-dimensional network of lithostratigraphic contacts and structures reveals large-scale structural and lithological patterns down to depths of  10 km, significantly improving our understanding of regional tectonic evolution. Beyond the resulting 3D model and its scientific outcomes, SA3D promotes a collaborative community of Alpine geologists and 3D geological modellers, setting the stage for continued for continued high-level research and exploration of the Alpine subsurface.