Electrical and Electromagnetic Methods in Geophysics

Electrical and electromagnetic methods probe the subsurface by exploiting contrasts in electrical conductivity, permittivity and magnetic permeability. Techniques span from direct‐current resistivity and self-potential surveys at low frequencies, through time‐domain and frequency‐domain electromagnetic (EM) induction, to natural‐source magnetotellurics (MT) and geomagnetic depth sounding. In each case, a primary field—whether injected current, time‐varying magnetic flux or natural geomagnetic variation—induces secondary responses in subsurface conductors. Measurements of voltages, magnetic perturbations or induced currents are then inverted via deterministic gradient‐based solvers or stochastic global optimisers to yield models of resistivity, chargeability or anisotropy. Advances in sensor design, array configurations and inversion frameworks have extended sensitivity to boulder‐sized conductors, deep geothermal reservoirs and distributed porphyry systems. Joint inversion with seismic, gravity or satellite gravity data reduces ambiguity, while time‐lapse surveys reveal dynamic processes such as fluid migration, recharge cycles and contaminant transport. Applications include mineral and hydrocarbon exploration, groundwater mapping, archaeological prospection, environmental monitoring and large‐scale crustal imaging. The integration of open‐source tools, high‐performance computing and machine‐learning surrogate models is now enabling rapid, robust and reproducible EM workflows across diverse geological settings.

Research from Nature Portfolio

A hybrid finite‐element mesh combining triangular prisms and tetrahedra has been developed for magnetotelluric forward modelling in rugged terrain. By refining only the near‐surface prism layers and coarsening deeper tetrahedral meshes, the approach delivers substantially higher accuracy for high‐frequency MT data with fewer degrees of freedom than conventional unstructured tetrahedral grids, reducing computational cost without sacrificing resolution.

A rapid imaging method for self-potential data interprets two-dimensional profiles by correlating the analytic signal of observed potentials with that of idealised dipole and monopole models. This technique extracts source depth, dipole moment and orientation in real time, proving robust against realistic noise levels and regional trends. Field applications to geothermal fields and mineral deposits yielded parameter estimates in close agreement with independent geological and geophysical constraints.

A pioneering marine self-potential survey at a back-arc hydrothermal field employed deep-towed electrode arrays to record continuous potential differences up to 50 m above the seafloor. The study revealed negative self-potential anomalies not only above visible vent mounds but also over flat sediments, demonstrating that fluid flow patterns beneath the seabed can be mapped effectively by passive SP measurements.

Electrical and Electromagnetic Methods in Geophysics publication trend

The graph below shows the total number of articles in electrical and electromagnetic methods in geophysics across all publications each year (not limited to Nature Index journals).

Technical terms

Electromagnetic induction: Generation of currents or fields in conductors by time‐varying magnetic fields.

Eddy current: Circular currents induced within conductive bodies, which produce secondary magnetic fields.

Self-potential (SP): Measurement of natural voltage differences caused by electrochemical or fluid flow processes.

Transient electromagnetic (TEM) system: Time-domain technique applying a pulsed primary field and recording decay of induced secondary fields.

Magnetotellurics (MT): Natural-source frequency-domain method recording electric and magnetic field variations to image deep resistivity structures.

Magnetic polarizability tensor (MPT): Rank-2 tensor characterising the linear response of an object’s induced magnetic dipole moment to an applied field.

Skin depth: Depth at which an EM wave’s amplitude decays to 1/e of its surface value, proportional to (ωμσ)⁻¹/².

Forward modelling: Simulation of EM responses from a hypothesised subsurface model.

Inversion: Computational adjustment of a model to minimise misfit between observed and predicted EM data.

References

1. Hybrid mesh for magnetotelluric forward modeling based on the finite element method. Scientific Reports (2023).
2. A fast imaging method for the interpretation of self-potential data with application to geothermal systems and mineral investigation. Scientific Reports (2023).
3. Marine self-potential survey for exploring seafloor hydrothermal ore deposits. Scientific Reports (2017).
4. Probing with Each Step: How a Walking Crab-like Robot Classifies Buried Cylinders in Sand with Hall-Effect Sensors. Sensors (2024).
5. Reduced order model approaches for predicting the magnetic polarizability tensor for multiple parameters of interest. Engineering with Computers (2023).
6. Underground Target Localization Based on Improved Magnetic Gradient Tensor With Towed Transient Electromagnetic Sensor Array. IEEE Access (2022).