S U M M A R YSince the decommission of the underground launching control room of the ground-based component of the French nuclear missile system, the whole installation has been turned into a cross-disciplinary underground laboratory. The LSBB is a unique low-noise underground laboratory because of its initial military conception and its location in the regional park of Luberon far from large cities, industry and heavy traffic. The deepest point is 500 m below the surface. At this depth a huge and non-conventional shielded cylindrical capsule is installed with no µ-metal, 1268 m 3 in volume, with a residual electromagnetic noise lower than 2 fT Hz −1/2 above 10 Hz. As a result, fluctuations of the Earth's magnetic field under 10 Hz can be recorded at a very low-noise level with a low-T c SQUID 3-D magnetometer. Taking advantage of the main gallery topology, a broad-band underground seismic array has been deployed since 2001. An analysis of data recorded simultaneously by the seismic underground array and by the magnetometer sensors during the Indian earthquake of 2001 January 26 is presented. Evidence of a magnetic field perturbation induced by the seismic waves at teleseismic distance (6250 km) is supported by a polarization analysis of seismic and magnetic signals. Spectral analysis shows specific frequency bands of perturbation related to physical processes such as ground water flow acceleration within the mountain structure.
Geophysical exploration is getting more and more difficult—many of the easily explorable
ore-bodies have been discovered and are already being exploited. Finding new mines
requires new technologies and tools. Transient electromagnetics (TEM) is widely used in
mineral exploration, but conventional sensors (especially induction coils) cannot fulfil the
needs anymore: deep targets, very conductive targets or targets under conductive
overburden are more easily (or sometimes only) detected using SQUIDs. In this paper we
will focus on low temperature SQUID magnetometers. As the systems are applied
worldwide it is necessary to strengthen them for all conceivable application scenarios. Here,
we report on the latest development of these systems which are now routinely
used in South Africa, Australia, Finland and Canada. This paper highlights the
main features of the system and describes one example from mineral exploration.
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