Electrical Resistivity Tomography (ERT).

Have you ever wondered how geophysics can help you on your project? Save on your drilling/excavation cost? Prevent field or site hazards? Carryout a geophysical investigation today before you proceed with your project. This article shares lot of insights into one of the popular geophysical exploration techniques with very vast applications – electrical resistivity imaging (ERI) or electrical resistivity tomography (ERT).

Theory and Principles:

Electrical Resistivity Tomography, or ERT, is a geophysical method that makes measurements on the ground surface by determining subsurface resistivity distribution. The technique is widely applied to mineral prospecting, hydrological or groundwater exploration, civil engineering, environmental investigation and archaeological mapping.

A multi-electrode resistivity meter is used to collect these ERT data using multiple electrodes planted on the ground to inject some electrical currents as signals into the ground and other electrode(s) to record the electrical potential difference developed within the chosen electrode configuration.


These measurements are being carried out on the surface along a line (3D grid can also be formed for a more comprehensive exploration project), the obtained potential difference data are then converted into apparent resistivities and used to make sounding curves and pseudo-sections. The apparent resistivity curves and pseudo-sections represents the resistivity changes of subsurface rocks, analysis of these plots, would enable us to find the subsurface resistivity anomalies or anomalous geologic structure.


The anomalous geologic unit could be metallic oxides, clay materials or sulphide minerals depending on the objective of the project. However, the resistivity of earth materials depends on different factors, such as, quantity and the chemistry of pore fluids, nature of the earth material, fluid saturation level. The Prescence of organic fluids, concentration of dissolved ions, weathering level of the rock unit, faulting, jointing and several other physical and chemical processes. Experienced Geophysicist can interpret the data, recommend depth and nature of anomalous units. A 3D survey can also help estimate the lateral extend or spread of the unit depending on the scope and objective of the project.


Electrical Resistivity Tomography or ERT is a very useful method in the world of geophysics. It is quite innovative and has made identifying the depth of anomalous geologic units, groundwater, detecting clays, and measuring conductivity in fluids an easy and hassle-free process. In our subsequent articles, we plan to share some of our site case studies with you.


Hephzibah Geosolutions provide geophysical exploration services for different applications and projects. Call us today to share your project with us and we would be more than happy to help.

Contact us today on: 520-451-5976 or email: info@hgeosolutions.com