What is VLF mapping?

I’vlfprofileve had the opportunity to get to know a few different consulting firms over the years and the one thing that stands out about THG Geophysics versus other firms is its commitment to try new applications and find the right fit to solve specific problems; even if it may seem off-the-wall.


This brings me to VLF mapping.  VLF is an acronym for very low frequency electromagnetics.   This geophysical technique takes advantage of the United States Navy’s very low frequency (VLF) shore radio signal, which provides continuous one-way communication to submarines in the Navy’s Fleet.


The geometry of the signal makes it optimal to induce signals into linear conductive features (such as high angled, water-filled fractures).  The measurement of a passive signal allows for quick, low-profile, data acquisition; which results in an inexpensive approach to fracture mapping.


So, why isn’t everyone doing this?  VLF data interpretation is a unique process which requires site knowledge and a strong understanding of the acquired data.  The technique also has several limitations; namely cultural noise.  A lack of understanding of these limitations typically results in poorly interpreted data, and hence poor results.  THG has extensive experience collecting and interpreting VLF data, and therefore can easily assess if it is the appropriate mapping technique for a client’s project.