Long-term monitoring successfully completed in the Tournemire underground laboratory

After several years of intensive fieldwork and development, the seismic monitoring program at the Tournemire Underground Laboratory in southern France—operated by the Institut de Radioprotection et de Sûreté Nucléaire (IRSN)—has been successfully completed. The project was coordinated by the 3D-US Lab in close collaboration with the "Seismic Hazards and Risk Dynamics," "Geomechanics and Scientific Drilling," and "Geoenergy" sections of the GFZ – Helmholtz Centre for Geosciences.

Final Measurement Campaign – Summer 2025

The program concluded with a comprehensive seismic campaign conducted from late June to early July 2025. This included both borehole measurements between existing horizontal boreholes and in-drift measurements. The objective was to investigate the structure and mechanical behaviour of the fault zone in claystone in detail, particularly following injection tests.

Modern equipment and advanced analysis techniques—such as a borehole seismic source and geophone chains—were utilized. These methods were developed and continuously refined over the years by the 3D-US Lab to ensure high-quality data and insights.

Monitoring Highlights of Recent Years

• 2021: Successful field validation of the newly developed SQ5 impact source prototype through initial seismic testing under real conditions.
• 2022: High-resolution seismic measurements conducted along drifts and within horizontal boreholes to image the fault zone structure in claystone.
• 2024: Hydraulic injection tests into the fault zone, accompanied by acoustic and seismic monitoring to assess mechanical responses.
• 2025: Final seismic monitoring campaign combining borehole and drift measurements to complete the long-term observation program.

Thanks to the successful completion of the latest measurements, a unique dataset has been obtained, capturing the temporal and structural evolution of a fault zone under the influence of injection tests. These results are highly significant for safety-critical applications such as the final disposal of radioactive waste, geothermal energy production, and underground storage. The interdisciplinary collaboration between GFZ, IRSN, and industrial partners like Amberg Technologies AG has demonstrated that innovative, targeted research under real underground conditions can make decisive contributions to our understanding of geomechanical processes.