Electrical resistivity methods are aimed for imaging subsurface structures when electrical current is injected into the ground through grounded electrodes on the surface or borehole.
DC resistivity methods are widely used to map lateral changes and subvertical objects such as fractures and intrusions.
These methods are divided into 2 major groups:
- Resistivity methods: vertical electric sounding (VES), electrical profiling, electric tomography (ERT), charge method.
- Methods of natural (SP – self potential) and induced polarization (IP).
How it works
The equipment set consists of powerful transmitter and low-noise receiver. Current is injected into the ground through grounded electrodes. In order to obtain information on resistivity, voltage is measured without switching the current off. In order to study polarization, the current is switched off and then the measurement is performed. For self-potentials measurement only a receiver is required.
ERT (electrical resistivity tomography) – high-resolution DC resistivity data processed using tomography technique. It allows to study in detail the electrical properties of the medium, to construct two-dimensional and three-dimensional models of distribution of resistance and polarizability, and to reveal local inhomogeneities of the section.
Depth of investigation (DOI) depends on electrode spacing. The greater the spacing the greater depth are reachable.
On a resulting cross sections resistivities and thicknesses of layers are presented. Borehole data can be assigned to geoelectric units. Low interference is present im case of grounded fences, operating power plants or power lines.
Collected data of currents and voltages is then converted to apparent resistivities. There are many factors that affect measurements such as:
- fluid saturation;
- fracturing of soils;
- fluid type;
- rock type.
- geological mapping (bedrock, fracture zones);
- lithologic section verification;
- karst areas delineation;
- landslides detection;
- deposits search;
- estimation of the depth water table depth, direction of groundwater detection and its velocity;
- archaeologic objects search;
- delineation of landfills, waste site characterization.