Electrical Resistivity Tomography
Also known as: ERT
Electrical Resistivity Tomography (ERT) is an active-source geophysical method that maps the spatial distribution of electrical resistivity in the subsurface by injecting current between two electrodes and measuring potential differences across an array of receiver electrodes. Advanced as a practical technique by Loke and Barker in 1996, ERT has become standard for hydrogeological, environmental, and structural characterization due to its sensitivity to fluid saturation and salt content.
Key highlights
- Excellent sensitivity to fluid saturation and ionic content, directly reflecting hydrogeological and contaminant conditions
- Flexible array geometries and electrode spacing allow targeting of specific depth ranges
- Can be deployed on surface, in boreholes, or in mines for flexible 2D/3D investigations
- High data density (hundreds to thousands of measurements) enable detailed spatial resolution
Intuition
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How it works
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When to use it
ERT is excellent for detecting groundwater saturation, mapping aquifer boundaries, and monitoring contaminant transport in environmental investigations. It is also useful for landslide hazard assessment, cavity detection, and geotechnical site characterization. Resistivity contrasts must be sufficient (typically >2:1) for ERT to resolve features. Combine ERT with seismic or borehole data for multi-parameter interpretation.
Strengths & limitations
- Excellent sensitivity to fluid saturation and ionic content, directly reflecting hydrogeological and contaminant conditions
- Flexible array geometries and electrode spacing allow targeting of specific depth ranges
- Can be deployed on surface, in boreholes, or in mines for flexible 2D/3D investigations
- High data density (hundreds to thousands of measurements) enable detailed spatial resolution
- Sensitivity decreases with depth; deeper structures require longer electrode spacings but lose lateral resolution
- Interpretation is non-unique; different resistivity distributions can produce nearly identical data
- High-conductivity surface layers (wet clay, salt) attenuate signals and obscure deeper structures
- Inversion algorithms are computationally demanding for large 3D datasets and may require damping to remain stable
Common pitfalls
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Applications
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Frequently asked
What is the difference between ERT and traditional vertical electrical sounding (VES)?
VES injects current at one pair of locations and measures potential at progressively larger electrode spacings, creating a 1D resistivity profile at one horizontal location. ERT uses fixed electrode arrays with multiple current injections and dense measurements, creating 2D or 3D resistivity distributions. ERT provides lateral structure; VES provides depth detail at a single point.
How deep can ERT investigate?
Approximate maximum depth is one-quarter to one-third of the total electrode array length. For a 100 m array, expect reliable imaging to 25–33 m. Achieving greater depth requires longer arrays, which increases survey time and cost. Borehole-based ERT can image deeper structures with shorter surface arrays.
How long does an ERT survey take?
Survey time depends on array length, number of electrodes, and the inversion software. A 1D sounding with 10–15 electrode spacings takes 30 minutes to 1 hour. A 2D profile with 48–64 electrodes can take 1–3 hours. 3D surveys can require many hours to days depending on spatial coverage and measurement density.
What electrode spacing should I use?
Electrode spacing is chosen based on the target depth and lateral resolution required. Smaller spacing (<1 m) resolves shallow features; larger spacing (>5 m) targets deeper structures but with reduced lateral resolution. Common spacings for hydrogeological investigations range from 2–10 m.
Sources
- 1.Loke, M. H., & Barker, R. D. (1996). Rapid least-squares inversion of apparent resistivity pseudosections by a quasi-Newton method. Geophysical Prospecting, 44(1), 131-152.
- 2.Telford, W. M., Geldart, L. P., & Sheriff, R. E. (1990). Applied geophysics (2nd ed.). Cambridge University Press.
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Cite this page
ScholarGate. (2026, June 3). Electrical Resistivity Tomography. ScholarGate. https://scholargate.app/geophysics/electrical-resistivity-tomography