Introduction
Geophysical electromagnetic exploration has emerged as a fundamental method in mineral exploration, geological mapping, groundwater detection, and environmental monitoring (Paine and Collins, 2003; Viezzoli et al., 2009; Delsman et al., 2018). Despite its widespread use, this technique faces ongoing challenges as the demand for greater exploration depth, higher data resolution, and more reliable interpretations continues to grow. Recent years have seen significant progress across both theoretical and technological fronts, driving the continuous evolution of innovative electromagnetic exploration methods, key technologies, and practical applications (Auken et al., 2015; Li et al., 2023; Zhang et al., 2025). At present, the field is undergoing a critical phase of development, marked by the deep integration of theoretical research, computational techniques, and engineering technologies. This convergence opens new avenues for tackling the increasingly complex challenges of subsurface exploration. The Research Topic Geophysical Electromagnetic Exploration: Theory, Technology, and Applications aims to comprehensively review and present the latest advancements in the field, focusing on key areas such as emerging theoretical frameworks, innovative numerical simulation methods, and advanced inversion techniques. This Research Topic includes 13 academic papers covering a wide range of cutting-edge topics, including fundamental anisotropic modeling, artificial intelligence-driven inversion, deep mantle imaging, and urban seismic risk assessment. Together, these contributions push the boundaries of innovation in the theoretical, methodological, and applied aspects of geophysical electromagnetic exploration.
Liu and Gao introduce a 3D finite-difference forward modeling algorithm for tensor-controlled source audio magnetotellurics (CSAMT) in axis-anisotropic media. Using this method, they conduct a comprehensive analysis of the characteristics of 3D tensor CSAMT responses in such media.
Wang et al. present a 3D staggered-grid finite-difference forward modeling algorithm for the Z-axis tipper electromagnetic (ZTEM) system. By coupling the Aggregation-based Algebraic Multigrid (AGMG) method with conjugate gradient iteration (AGMG-CG), they achieve significantly accelerated solutions for large-scale systems compared to the traditional QMR method.
Li et al. adopted the SUTEM, successfully addressing the technical challenge that traditional electrical methods are susceptible to low-resistivity shielding from shallow aquifers. Combining FDTD numerical simulation with field tests in the Ningdong mining area, the study drew the core conclusion: when receiving devices are located on the surface, the thickness and depth of shallow aquifers significantly interfere with the detection signals.
Aohuai et al. introduce a fast time-domain electromagnetic (EM) inversion method that integrates prior constraints and convolutional neural networks (CNN) for dynamic monitoring of the electrical properties of vertical transverse isotropy (VTI) shale reservoirs during hydraulic fracturing. This method has the potential to become a core technology for geophysical monitoring of unconventional oil and gas reservoirs and to support the efficient and sustainable development of shale gas resources.
Gao et al. propose the Wide-Field Electromagnetic Method (WFEM) for monitoring deep hot dry rock hydraulic fracturing beneath thick, low-resistivity overburden layers (>4,000 m). Through 3D forward modeling, they optimize key acquisition parameters (transmitter-receiver distance, current, electrode spacing) to maximize sensitivity to resistivity changes induced by conductive fracturing fluids.
Sánchez and Gallardo investigate the often-neglected role of magnetic permeability in ground-penetrating radar (GPR) signal propagation. They develop a finite-difference time-domain (FDTD) algorithm that fully accounts for heterogeneities in dielectric permittivity, electrical conductivity, and magnetic permeability. The study argues for the inclusion of magnetic permeability in high-frequency EM modeling and the potential benefit of measuring both electric and magnetic field components.
Li et al. utilize a dense 3D magnetotelluric (MT) array to investigate the deep seismogenic environment of the Huaibei Plain Fold Belt in eastern China. High-quality resistivity models reveal distinct high- and low-resistivity structures, with crustal low-resistivity anomalies linked to tectonic fluids and deformation. The results indicate a seismogenic setting capable of generating strong earthquakes, primarily driven by horizontal tectonic forces, with no significant mantle upwelling influence identified. This work provides crucial insights for regional seismic hazard assessment.
Ma et al. present a three-dimensional geomagnetic depth sounding (GDS) study that images the mantle conductivity structure beneath eastern China using long-period geomagnetic observatory data. A key methodological advance of this work is the explicit incorporation of realistic surface conductance derived from global land–ocean distributions, which effectively mitigates ocean induction effects that commonly distort long-period C-responses. The resulting 3-D conductivity model reveals prominent conductive anomalies in the mantle transition zone and uppermost lower mantle beneath the Bohai Bay, North China, and the South China Sea–Hainan region. This study demonstrates the capability of high-resolution regional-scale 3-D GDS inversion to resolve deep mantle electrical heterogeneity and provides new constraints on subduction-related geodynamic processes beneath eastern China.
Castillo-Reyes et al., present a systematic review and bibliometric assessment of inverse geo-electromagnetic (EM) modeling. It comprehensively evaluates deterministic, stochastic, and machine learning-based inversion methods, analyzing their principles, applications, and limitations. Utilizing bibliometric tools and unsupervised neural networks, the study identifies key trends, global research contributions, and emerging topics such as deep learning. The work offers an integrated overview to guide future research in geophysical exploration.
Huang et al. were the first to fully disclose the independently developed fixed-wing time-domain airborne electromagnetic system (iFTEM-II). This system features key innovations, including high-power transmission technology that generates kiloampere-level currents for deep penetration, and a specially modified flight platform with an externally mounted flexible transmitting coil and long-suspended receiving cabin. Additionally, the system incorporates advanced signal processing techniques for extracting weak nanovolt-level signals in high-interference environments. Field testing has demonstrated that the system can achieve an effective detection depth of up to 600 m.
Hu et al. conducted an integrated geophysical-geological study for the peripheral exploration of the Dapai Fe-polymetallic deposit. High-precision ground magnetic data and magnetization vector inversion delineated the NNW-trending structural framework and identified prospective zones, which were subsequently verified by drilling to reveal multi-layer orebodies and associated intrusions at depth. This work establishes a practical prospecting model, demonstrating the effectiveness of integrated interpretation for deep and peripheral exploration of similar Makeng-type deposits.
Liu et al. investigate the low-temperature magnetic properties of deeply buried gas hydrate-bearing sediments from the Hikurangi subduction zone. Using advanced low-temperature magnetometry, the authors reveal how magnetic minerals such as magnetite and greigite are preserved or transformed under reducing diagenetic conditions. Their work not only provides insights into magnetic mineral evolution in hydrate systems but also establishes a “magnetic fingerprint” methodology for identifying fossil gas hydrate zones, offering a novel tool for paleoenvironmental reconstruction and resource exploration.
Zhou et al. addresses the challenge of electrical anisotropy in subsurface media—a common yet often overlooked complexity in geophysical surveys. The authors develop a 3D forward modeling algorithm for surface-borehole azimuthal induced polarization in principal axis anisotropic formations. This study enhances the theoretical foundation of borehole electromagnetic methods and provides critical guidance for data interpretation in anisotropic geological environments.