SQUID magnetometer used in geothermal survey

A three‐axis dc SQUID magnetometer with a sensitivity of ${10}^{\text{−14}}$ tesla ${\mathrm{Hz}}^{\text{−1/2}}$ has been used in a magnetotelluric survey that has revealed an anomaly in the apparent resistivity near Leach Hot Springs in Grass Valley, Nevada. In magnetotellurics, fluctuations in Earth’s magnetic field and in the electric field induced in the ground are measured simultaneously. From these data, the apparent resistivity of the ground as a function of frequency can be computed. The survey was conducted by John Clarke and Frank Morrison of Lawrence Berkeley Laboratory and their collaborators. In principle, the group says, the technique has the capability of detecting geothermal sources as much as a few tens of kilometers below Earth’s surface. Electromagnetic methods are useful in identifying the position, depth and extent of a geothermal reservoir.