Vertical Electrical Sounding (VES)
A Vertical electrical sounding (or VES) is a 1D resistivity method that provides deep information of the subsurface with minimal equipment and personnel. It is one of the oldest methods for acquiring resistivity and one of the least expensive to conduct per unit depth. The VES method can be quite versatile for reconnaissance surveying or when there are equipment limitations. The data from vertical electrical sounding are more sensitive to general electrical structure than other 1D electromagnetic methods, such as TDEM, because high resistivity contrasts are better resolved with VES.
The VES method is quite versatile for reconnaissance surveying or when there are equipment limitations. HGI typically conducts vertical electrical soundings alone or in conjunction with other methods, such as microgravity or induced polarization.
The example below shows VES data acquired in the Atacama Desert of northern Chile. The plot highlights raw data, inversion model fit to the raw data, and the resulting 1D resistivity-based stratigraphic interpretation.
HGI has conducted VES surveys alone and in conjunction with other methods, such as microgravity or induced polarization. For example, the gravity information can be used to map the geometry of a basin while the 1D resistivity data can provide the stratigraphic structure and location of evaporites.
1D resistivity soundings can also be modeled together as a two-dimensional resistivity profile under certain conditions. In this way, the model produced from the data can be combined into a single coherent understanding of the subsurface. The example below shows an 11-mile cross section (18,000 m) through a basin in the southwestern United States. Eleven vertical electrical soundings were acquired and each location of the transmitter and receiver were recorded to ensure proper geo-referencing into the inversion software. The results show coherent layering across the profile and these data can be used to interpret faults, bedrock, and clay lenses.