VLF Surveys

VLF Geophysical Survey

Very Low Frequency Electromagnetics (VLF) is a geophysical technology for ground probing that employs VLF signals in the 15 to 30 kHz range, typically used for submarine communication. This signal is effective for conducting geophysical measurements worldwide.

VLF is an electromagnetic method that depends on transmitted currents inducing secondary responses in conductive geological units. A VLF anomaly indicates a change in the orientation of the electromagnetic vector over conductive subsurface materials.

Airborne VLF data are primarily used to interpret large-scale geological features such as faults and conductive rock units. However, under favorable conditions, smaller conductors, like those caused by sulfide mineralization, may also be detected. VLF data are considered an excellent, cost-effective supplement to airborne magnetic data.

In mineral exploration, VLF data are utilized to map geological structures, including the apparent dip of fault zones and shear zones. The data can be interpreted to determine the dip of these structures for accurate drilling. Additionally, the data help identify conductive ground that might indicate sulfide concentrations. A third application is mapping overburden in preparation for drilling and further sampling.

In groundwater exploration, VLF is crucial. It can detect conductive bodies of fluid—such as water—in bedrock or near fractures. Another application is contaminant mapping, as contaminants may have higher resistivity than surrounding fluids due to solid inclusions in the fluid.