EMSCOPE MT Backbone (permanent) Stations

MT Backbone (MT BB) stations consist of two 2-m deep, 30 cm diam vaults buried underground, separated by 5 m, or in one case, two insulated above-ground instrument vaults. One vault holds a fluxgate magnetometer sensor, and the other vault holds a data acquisition/recording system. Electric fields are recorded by measuring the potentials across Pc-PbCl2 electrodes contained within salt supersaturated kaolin slurry-filled vaults, buried 1 m below ground, and separated by distances as great as 4 km in some cases. These define pairs of N-S and E-W oriented electric dipole receivers. Backbones sites are solar powered and designed to operate for years of continuous use.

The orange cross symbols in the map below mark the location of EMScope MT backbone stations. The satellite dish symbols are permanent magnetic observatories. Seven MT BB stations are installed. These are in: Parkfield California; Soap Creek, near Corvallis Oregon; Braden, south of Springfield Missouri; Socorro New Mexico; Blacksburg Virginia; near Angela Montana; Agassiz National Wildlife Refuge near Thief River Falls Minnesota. The dark red cross is the location of an existing, pre-EMScope ultra-long period MT data set from the Canadian Shield.

The MT BB instruments are specially-packaged Narod Geophysics NIMS systems (or, for Blacksburg Virginia, a Space Research Institute, Lviv Ukraine LEMI system), configured for installation into underground vaults, or for the LEMI, above-ground insulated vaults. Each of the long cylinders in the foreground of the photo below is a triaxial ring-core fluxgate sensor, and each of the shorter, larger diameter cylinders in the background is a NIMS data acquisition system.

The typical BB MT site uses two 30 cm diameter, 2-m long vaults. One contains the NIMS magnetometer sensor, and the other the data acquisition system. Four other vaults 15 cm in diameter hold a set of 1-m long, 10-cm diameter electrode containment vessels, each of which is filled with salt super-saturated kaolinite slurry, contained within a slurry-filled bucket in the bottom of the hole drilled for the electrode vault. Electrical contact is made between the electrode within the containment vessel, and the earth pressed around the top annulus of the slurry-filled bucket.