3D Ambient Noise Tomography for Preliminary High-Resolution Geological Surveys of Hydropower Dams – The Rhonergia Case Study (France)

3D Ambient Noise Tomography (ANT) is a powerful, non-invasive method for imaging the shallow subsurface, offering a detailed understanding of geological structures relevant to geothermal and geological prospection. This paper presents the application of Sixense SISSTERRA solution in a project where more than 1,100 seismic sensors, including aquatic nodes, were deployed across three zones near the Rhône River. The objective was to delineate sedimentary structures, identify quaternary-tertiary transitions, and assess geotechnical risks. The use of underwater nodes in the Rhône enhanced spatial coverage and demonstrated the method’s applicability in hydrologically complex areas. The data collected from ambient noise was processed to produce a 3D shear wave velocity (Vs) model, reaching depths up to 60 meters. This model enabled identification of lateral and vertical heterogeneities, highlighting areas of potential permeability or instability. Compared to traditional geophysical approaches, this technique delivers broader spatial coverage and higher-resolution imaging of subsurface features essential for early-stage geothermal site evaluation.