Large N-array and DAS around the Lavey geothermal reservoir in Switzerland in challenging topographic settings

SUMMARY From April until the end of June 2025, we deployed a dense seismic network of 271 three-component stations within an 8 km radius around Lavey-les-Bains, Switzerland, to investigate the structure of the country’s hottest known natural geothermal system. The site hosts a 3 km-deep exploration well (Lavey-1), drilled in 2022, that revealed unexpectedly low flow rates despite temperatures exceeding 120°C, prompting the suspension of the project. The site lies within the narrow Rhône Valley, characterized by steep topography, strong lateral structural heterogeneity and elevated anthropogenic noise, complicating seismic imaging. The dense nodal array was complemented by a distributed acoustic sensing (DAS) system along a buried telecommunication cable, providing a hybrid data set suited for passive seismic imaging. We describe the network geometry, instrumentation and deployment logistics; assess data completeness and noise characteristics and present first examples of ambient noise and earthquake recordings. Preliminary analyses demonstrate a high data quality and spatial coverage. This experiment establishes a benchmark data set for developing advanced passive imaging techniques in complex Alpine environments.