Communication Dans Un Congrès Année : 2002

The Laboratoire Souterrain Bas Bruit (lsbb) In Rustrel-pays D'apt (france): A Unique Opportunity For Low-noise Underground Science

Résumé

The former underground lauching control room 1 of the ground based component of the french nuclear missile system has been decommissioned. This installation has been designed and built to remain operational even in case of a near-by nuclear blast. As a result it is robust to radioactive clouds, thermal and mechanical waves as well as electromagnetic pulses. The whole installation has been turned progressively into a cross disciplinary underground laboratory LSBB. LSBB is, so far, a unique low noise underground set-up because of its initial conception and its location in the regional parc of Luberon far from large cities, industries and heavy car traffic. The galleries of LSBB, horizontally accessible from the surface, are buried in the south of the Albion Plateau, northward Aix-en-Provence. Their ensemble is almost flat with a 2% slope and a total length larger than 3.5km under the karstic calcareous "Grande Montagne". The deepest point is 500m below the surface. At this depth, a huge and non conven- tional shielded cylindrical capsule with an horizontal axis was installed. It measures 28m long with 9m in diameter surrounded by 1cm of stainless steel plus 2m of rein- forced concrete. This is indeed a very large Faraday cage but with µmetal, 1250m3 no in volume with a residual electromagntic noise lower than 2fT/ Hz above 10Hz, the present limit of the residual noise of the SQUID magnetometer we have used. As a result, earth magnetic field fluctuations can be recorded even at a very low noise level with SQUIDS (superconducting quantum interferometric devices) at liquid he- lium temperature. Taking advantage of the "V" geometry of the main gallery, a broad- band underground seismic array has been designed with 5 STS2 sensors and is de- ployed since the beginning of 2001. Simultaneously, magnetic measurements are done with a low Tc SQUID magnetometer jointly to the seismic recordings. The spectral noise calibration of the LSBB will be presented and discussed as well as the prelim- inary analysis of the data recorded simultaneously by the seismic underground array and by the magnetometer sensor during the Indian earthquake of january 26th, 2001 Magnetic field perturbations induced by the seismic wave propagation at teleseismic distance (approx. 6500km) were measured.
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hal-04751690 , version 1 (24-10-2024)

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G. Waysand, S. Gaffet, J. Virieux, A. Chwala, M. Auguste, et al.. The Laboratoire Souterrain Bas Bruit (lsbb) In Rustrel-pays D'apt (france): A Unique Opportunity For Low-noise Underground Science. EGS XXVII General Assembly, 2002, Nice, France. ⟨hal-04751690⟩
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