f Electromagnetic horizontal-loop-measurements in the salt mine of Bischofferode (Germany)

Dry rock salt with resistivity higher than 10-4 Ωm is undetectable with electromagnetic methods and can be considered as an insulator. On the other hand, the resistivity of brine (0.03 Ωm) is low and unlike dry rock salt a good conductor. This high resistivity contrast will be used to locate brine soaked areas or filled fissures, They imply a high risk of brine penetration and can cause fatal tunnel collapse.