VLF-EM
The VLF (very low frequency) method is an electromagnetic method that uses as a transmitting source radio frequency waves in the range of 10 kHz to 30 kHz, which are commonly broadcast by local stations around the world. The method measures the secondary magnetic field produced by eddy currents that are induced in the ground due to the presence of VLF waves and is suitable for detecting conductive structures up to 200 m deep in terrain with high electrical resistance.
The method acquisition consists of detecting, by means of the VLF receiver, the frequency and direction of the transmitting waves. Then the receiver is properly oriented through the survey lines, with reading intervals between 5 m to 25 m, in order to detect the response of the electromagnetic anomalies in the ground. Through analysis, 2D modeling and interpretation, the VLF method allows the location of shallow conductors, structural mapping (faults, shear zones) and geological mapping (geological contact, dykes, veins, faults, etc).