Simultaneous geomagnetic monitoring with multiple SQUIDs and fluxgate sensors across underground laboratories

For two periods of several weeks duration in spring and autumn 2014, we monitored fluctuations in the geomagnetic field using 3-axis SQUID magnetometers at three locations within the LSBB tunnel network. Measurements at the water flow point C, and the GAS gallery supplemented the measurements by the permanent [SQUID] 2 system in the Capsule. The frequency spectra of the magnetic fluctuations varied considerably between the three locations. These measurements have provided a unique data set to investigate the potential of underground SQUIDs to monitor the gradient of geomagnetic signals and thus investigate magnetotelluric effects and possible seasonal effects due to changes in the water content of the surrounding rock. We also compared the measurements of a SQUID and fluxgate system, and report on fluxgate measurements at the Boulby Underground Laboratory.