From Seismic Characterization to Coupled Process Testing Along Drifts at LSBB as an Example of Establishing an International Facility for a Worldwide Network of Underground Research Laboratories

The Laboratoire Souterrain à Bas Bruit (LSBB) at Rustrel France is a French National Instrumented Infrastructure, CNRS, dedicated to inter-Disciplinary Underground Science and Technology. The underground galleries and the surrounding carbonate rock formations are well characterized by seismic imaging studies obtained with sensors both along the ridges and underground along the drifts. The facility is horizontally accessible with the main tunnel following an L-shape. The deepest is 518m below the surface. The main tunnel continues with a long gallery below the ridge, and ends with an escape shaft to the surface. Electrical and fiber optic communication cables connect the galleries and the underground to the huts on the surface. All data from LSBB are distributed on line (http://lsbb.oca.eu) and data from the 3D broadband seismic array are fed in real time (delay of ~4s) to the European Union seismic network (see streams RUSF_01, 03, 04, 05, 06, and 07 at http://www.orfeus-eu.org/Data-info/orbstats.html). Concurrently with establishing the seismic network, the LSBB characterizes its low noise environment, including its low ambient magnetic noise with a (SQUID)2 magnetometer, located 518m below the surface in a shielded cage. The magnetic noise floor in the cage is lower than 2fT/SQRT(Hz). Together with the seismic network and the magnetic sensor, tiltmeters, radiation sensors, groundwater pressure and chemistry monitoring devices are installed to characterize the unsaturated environment along the tunnel. Seasonal seepage observations are also collected. 3 national research projects are currently carried out along dedicated tunnels: (1) the project on High-Pulse Poroelasticity Protocol (HPPP) for geophysical monitoring of CO2 injection in reservoirs (http://hppp.unice.fr/), focusing currently on hydromechanical testing in carbonate rock; (2) the MAXWELL electromagnetic project on broadband imaging which employs joint resistivity and permittivity inversion (http://lsbb.oca.eu/spip.php?article46); and (3) the project LINES on fiber optic instrumentation to detect small vibrations and deformations (http://lsbb.oca.eu/spip.php?article99). The LSBB, under continuous improvement, is an underground laboratory dedicated to the permanent observation of coupled processes in the shallow crust. The results obtained at LSBB contribute to the knowledge of the solid Earth and space physics. The escape tunnel at the end of the tunnel network is used for hydrogeological monitoring. We plane to use this space and new vertical boreholes for CO2 injection studies in that carbonate rock medium. Carbonate reservoirs play a crucial role in the analysis of water resources, petroleum reserves, and CO2 and other fluids sequestrations. These studies are pursued worldwide, including the ones planned in the USA’s Deep Underground Science and Engineering Laboratory in metamorphic rock. We plan to expand our collaborations between laboratories to include other underground research facilities and collectively pursue international, interdisciplinary initiatives, leading to innovation in energy, water resource, and environmental studies.