The research, published in the journal Discover Soil, was carried out by Donald Okechukwu Nnebedum of the Department of Geology at the University of Nigeria, Nsukka. The target was an edifice approaching completion in the Nsukka urban area, where fractured foundation soils had been suggested as a primary cause of structural distress. The site sits within the Campano-Maastrichtian succession of the Anambra Basin and is underlain by the Maastrichtian Ajali Formation, a unit composed of medium to coarse-grained sandstones and conglomerates, including angular to subangular quartz-arenites. Fresh samples of this formation are typically whitish with iron staining, but weather to a brownish colour at the surface, a sign of its high iron content. Outcrop evidence suggests the formation is between 25 and 50 metres thick, with fluvio-deltaic and fluvial channel depositional features such as trough and planar crossbedding, mud-draped foresets, and Ophiomorpha trace fossils.

Crucially, the region has a documented history of tectonic deformation. Post-Santonian events have left two fracture trends, trending northwest-southeast and northeast-southwest, in the Campano-Maastrichtian formations around nearby Enugu. These pre-existing weaknesses matter because even though cohesionless coarse-grained sandstones have lower bearing pressure limits of about 440 kilopascals, and medium-grained sandstone soils about 240 kilopascals, fractures can slash that strength dramatically, posing an extreme threat to any structure founded directly above them. Classical bearing capacity analyses, such as Prandtl’s and Terzaghi’s methods, assume a homogeneous soil mass and may simply miss fracture-induced heterogeneity altogether, which is precisely where geophysics earns its keep.

The study deployed two techniques side by side on identical survey plans. Electrical resistivity imaging, or ERI, is the established workhorse for mapping near-surface inconsistencies, and its effectiveness in fracture detection is well documented. Its companion, induced polarization imaging, or IPI, measures a subtler phenomenon. When current is injected into the ground and then abruptly switched off, the measured voltage does not vanish instantly. A residual polarization voltage, known as overvoltage, decays over time as electrical charges stored in the subsurface gradually dissipate. The magnitude of this effect, expressed as chargeability in milliseconds, reflects how well the ground acts like a capacitor. In non-mineralized soils, this response arises from electrolytic or membrane polarization, in which positively charged ions concentrate at electrolyte boundary layers and extend along the pore walls of clastic rocks.

That physics is exactly what makes the method sensitive to fractures. Open fractures enhance porosity and create conduits for fluid movement, and the groundwater filling them behaves as a weak electrolyte rich in dissolved minerals. Fracture zones therefore act like capacitors, accumulating charge that decays slowly once the current is cut off, producing anomalously high chargeability. Fractures that juxtapose two separate blocks or bring chemically dissimilar fluids together can amplify the effect further, and even clay-filled fractures generate a polarization response when current is interrupted. According to Archie’s law, which governs electrolytic conduction in clastic rocks, increasing porosity also drives down bulk resistivity, so fractured zones should appear as abrupt low-resistivity features in resistivity images. The two techniques thus provide independent, complementary fingerprints of the same geological defect.

Four ERI surveys and four IPI surveys were executed along parallel lines crossing the foundation zone, using the same Wenner alpha electrode configuration for both. A base electrode spacing of 10 metres was expanded through separation factors of one, two, and three, reaching a maximum spacing of 30 metres and a median depth of investigation of about 15.57 metres, adequate for non-high-rise foundation studies. Data were acquired with an ABEM SAS 1000 Terrameter configured for simultaneous resistivity and time-domain induced polarization measurement, offering resistivity accuracy of about one percent and chargeability precision of 0.1 milliseconds. Stainless steel electrodes kept contact resistance below 5 kilo-ohms, current injection ranged from 50 to 150 milliamperes, and four to eight stacking cycles per reading boosted the signal-to-noise ratio, with reciprocal measurements on ten percent of data points confirming repeatability errors below three percent. Current and potential cables were routed separately to suppress electromagnetic coupling, a refinement previously shown to improve time-domain IP data quality in multi-electrode systems.

The raw apparent resistivity and apparent chargeability data were organized in block model format and inverted with a least-squares approach using RES2DINV software, a format noted to deliver good solutions for fault modelling. Reliability was assessed carefully. A depth of investigation index, computed by comparing inversions initialized with reference half-spaces of 100 and 1000 ohm-metres, indicated values below 0.2 and therefore well-resolved model parameters to depths of 12 to 14 metres, comfortably enclosing the interpreted fracture zones at 5 to 12 metres depth. Interpreted fracture positions carry lateral uncertainty of roughly 1.5 metres and depth uncertainty of about 1 metre, while absolute resistivity and chargeability values vary by roughly 12 to 18 percent and 9 to 15 percent respectively. Importantly, the spatial coincidence of low-resistivity and high-chargeability anomalies remained stable across perturbation tests.

The results were emphatic. On survey line one, the inverted resistivity section revealed an inclined zone of low resistivity, below 600 ohm-metres, at offset distances of roughly 70 to 90 metres, and the corresponding chargeability image showed an anomalously high zone of 7.77 to 8.98 milliseconds against a background of just 0.5 to 3.0 milliseconds at the same position. Survey line three, on the opposite side of the site, mirrored the pattern, with a low-resistivity anomaly near 203 ohm-metres or less between 75 and 105 metres and high chargeability of 11.6 to 24.8 milliseconds between 80 and 105 metres. Together, the paired lines outlined a fracture trending north-northwest to south-southeast, dubbed the Alpha fracture. Survey lines two and four mapped a second defect, the Beta fracture, trending northeast-southwest, with line two showing resistivity anomalies from 107 to 695 ohm-metres and chargeability from 200 to 395 milliseconds, and line four showing resistivity of 169 to 388 ohm-metres and chargeability between 195 and 296 milliseconds, plus a smaller zone exceeding 603 milliseconds. Signal-to-background ratios for all IPI anomalies exceeded the accepted threshold of 2.0, confirming that the signatures were genuine subsurface features rather than noise artifacts.

The decisive test came from the ground itself. A post-survey site visit revealed pronounced fissures on the foundation floor at the same spatial locations the imaging had flagged, with one set trending north-south, consistent with the Alpha fracture, and another set trending east-west, matching the Beta fracture. These surface expressions tally with the two post-Santonian fault trends previously identified in the Campano-Maastrichtian formations of the Anambra Basin. The study’s multi-evidence framework, combining co-located anomalies, stable inversion convergence, cross-line replication, and surface correspondence, demonstrates that conventional two-dimensional time-domain induced polarization imaging, a cost-effective and easily deployed technique, can stand shoulder to shoulder with electrical resistivity imaging in mapping fracture-induced heterogeneity beneath foundations. The author notes that future work should incorporate targeted borehole data to link geophysical responses directly to specific fracture properties, but for engineers worried about what lurks beneath their next project, the message is clear: the ground has an electrical memory, and it will tell you where it is broken.

Subject of Research: Use of 2D induced polarization imaging to detect fractures in foundation soils at a failing building site in Nsukka, Nigeria

Article Title: Efficacy of 2D induced polarization in detecting fractures in foundation soils

Article References: Nnebedum, D. O. (2026). Efficacy of 2D induced polarization in detecting fractures in foundation soils. Discover Soil, 3(1), Article 108. https://doi.org/10.1007/s44378-026-00268-z

Image Credits: AI Generated

DOI: 10.1007/s44378-026-00268-z

Keywords: induced polarization, electrical resistivity imaging, foundation soils, fractures, geophysics, Nsukka, Anambra Basin, Ajali Formation, chargeability, Wenner array, site investigation, building failure

Researchers led by Bomi Kim of the Korea Institute of Geoscience and Mineral Resources, together with colleagues at Kongju National University, turned their attention to the Myeonsan titanium deposit in the Taebaeksan Basin of eastern South Korea. The deposit, hosted by the Cambrian Myeonsan Formation, is interpreted as a paleo-placer: titanium-bearing minerals such as rutile, ilmenite, and hematite were eroded from Precambrian basement rocks, transported by ancient rivers, and concentrated in conglomeratic sandstone during sedimentary deposition. Because the ore horizons are surrounded by a diverse suite of lithologies, including limestone, clastic sedimentary rocks, intrusive dykes, and granite, the site provides an ideal natural laboratory for testing which physical measurements can reliably separate ore-bearing rock from barren host rock.

The team selected 39 representative drill-core samples from borehole KDMS 2023-10, which penetrates the mineralized interval and its surroundings. The samples were divided into five groups: nine Myeonsan ore specimens, twelve limestones, four dyke rocks, eleven clastic sedimentary rocks, and three granites. Each specimen was prepared as a polished cylinder, a geometry that promotes uniform current distribution and simplifies the calculations needed for electrical measurements. Where core material was scarce, half-core semi-cylindrical specimens were prepared for the titanium ores, ensuring that every sample could pass through the full battery of tests.

That battery was deliberately broad. The researchers measured density and porosity using the Archimedes buoyancy method, following International Society for Rock Mechanics procedures: specimens were dried at 110 degrees Celsius for 24 hours, vacuum-saturated with water, and weighed in both saturated and submerged states. Magnetic susceptibility was recorded with a Bartington MS-3 meter at six positions on each sample to average out mineralogical anisotropy. Direct-current electrical resistivity, time-domain induced polarization (TDIP), and electrochemical impedance spectroscopy (EIS), known in geophysics as spectral induced polarization or SIP, were measured on fully saturated specimens using Solartron instruments with copper-mesh and filter-paper electrodes. Portable X-ray fluorescence (p-XRF) provided elemental compositions, and petrographic thin sections revealed the mineralogical texture behind the numbers.

The results deliver a clear hierarchy of diagnostic power. Density proved the most straightforward discriminator: the titanium ores averaged 3.17 grams per cubic centimeter, well above limestone at 2.74, dyke rocks at 2.73, clastic sediments at 2.84, and granite at 2.68. The elevated density reflects the abundance of heavy oxide minerals such as rutile and ilmenite packed into the ore horizons. The larger standard deviation among ore samples also revealed heterogeneous mineral enrichment within the mineralized interval, a useful warning that ore grades can vary significantly over short distances.

Chargeability, the capacity of a rock to store and slowly release electrical charge, produced an even more dramatic contrast. The ore samples averaged 91.57 millivolts per volt, roughly sixteen times higher than limestone at 5.64, dyke rocks at 3.41, clastic sediments at 4.62, and granite at 6.56. This signal arises because semiconductive ore minerals accumulate charge at mineral-fluid interfaces when an electric current is applied, then release it gradually after the current stops. In practical terms, an induced-polarization survey over this deposit should light up the ore zones while leaving most host rocks nearly invisible, making TDIP one of the most valuable exploration tools for sedimentary titanium deposits.

Not every measurement proved useful, and the negative results are as informative as the positive ones. Porosity values, ranging from 0.36 to 1.19 percent across groups, showed no meaningful separation between ore and host rocks, reflecting instead the compaction and cementation history of the sedimentary sequence. Magnetic susceptibility failed as a discriminator because the ore assemblage itself is magnetically quiet: rutile is only weakly magnetic and hematite is antiferromagnetic, so the intrusive dyke rocks, averaging 10.00 millisiemens per meter, outmagnetized the ores at 2.82. Electrical resistivity was similarly ambiguous, controlled mainly by pore structure and water saturation rather than ore content, with dyke and granite samples showing lower resistivities than the ores themselves.

The frequency-domain measurements added a powerful new dimension. In EIS spectra, several ore specimens, including MO1, MO2, MO5, and MO9, displayed strong phase responses at low frequencies below about 100 hertz, a signature of interfacial polarization between semiconductive ore minerals and pore fluids. These same samples showed the highest TDIP chargeability and elevated titanium contents above 3.11 weight percent and iron above 8.82 weight percent. Other ore samples and most host rocks instead showed phase values that increased toward higher frequencies, a pattern associated with dielectric polarization in insulating silicate and carbonate minerals. The two spectral fingerprints give geophysicists a way to distinguish genuine ore polarization from background dielectric effects, sharpening the interpretation of field survey data.

Petrography tied the physics back to mineralogy. Under the microscope, the ore specimens were dominated by opaque rutile, ilmenite, and hematite with minor quartz, while limestones were composed of calcite, dyke rocks of quartz, feldspar, and amphibole, clastic sediments of alternating coarse and fine silicate grains, and granites of quartz, feldspar, mica, and tourmaline. Sericitization of feldspar in the dykes and granites pointed to hydrothermal alteration. These observations directly explain the measured contrasts: dense, polarizable oxide minerals produce high density, high chargeability, and strong low-frequency phase responses, whereas insulating silicate and carbonate host minerals generate only weak, high-frequency dielectric behavior.

The study also exposed practical limits. One ore specimen, MO3, contained the highest titanium (9.85 weight percent) and iron (24.27 weight percent) of all samples yet showed weaker polarization than its peers, likely because p-XRF was measured at a single spot on a heterogeneous specimen. Because the core samples had to be preserved intact for the mining project, destructive analyses such as X-ray diffraction and ICP-MS were not possible. The authors conclude that spot geochemistry is best used to flag the presence of metallic minerals, while volume-integrating measurements such as density, TDIP, and EIS provide the more robust bulk characterization. Together, the integrated dataset establishes quantitative criteria for distinguishing titanium-bearing rocks from their hosts and demonstrates how combined petrophysical, geochemical, and mineralogical measurements can sharpen the search for a critical mineral whose secure supply increasingly depends on finding it faster and smarter.

Subject of Research: Integrated physical property measurements of titanium-bearing ores and host rocks at the Myeonsan deposit for mineral exploration

Article Title: Integrated physical property measurements of titanium-bearing and host rocks for mineral exploration

Article References: Kim, B., Shin, S., Shin, D., & Lee, G. (2026). Integrated physical property measurements of titanium-bearing and host rocks for mineral exploration. Environmental Earth Sciences, 85(16), Article 405. https://doi.org/10.1007/s12665-026-13140-8

Image Credits: AI Generated

DOI: 10.1007/s12665-026-13140-8

Keywords: titanium, mineral exploration, Myeonsan deposit, induced polarization, spectral induced polarization, density, chargeability, paleo-placer deposit, petrophysics, critical minerals, South Korea, rutile