Impedance Tomography Research Articles

An Attempt to Delineate Subsurface Ain Aldawar Cavity Using 2D Electrical Resistivity Imaging Method in Haditha Area, Western Iraq

The current study used 2D resistivity imaging to identify a shallow subsurface cavity in Haditha, western Iraq. The cavities and voids near the surface restrict land use and create a variety of geotechnical hazards, such as land subsidence, infrastructure damage, and structural cracks. As a result, the presence of an underground weak zone is a major concern for engineers before beginning any development, given the risk of future disasters. The four 2D resistivity traverses in this study were carried out using a dipole-dipole array with a - spacing of 3 m and an n-factor of 6. The data was inverted using RES2DINV software, which employs robust inversion methods. The 2D inverse model reveals a shallow cavity ranging from 5 to 12 meters and a width of around 40 m.

Searching for ancient pits and voids at the Ouels Mine (Castel-Minier, France) by using geophysical methods

A map from the early twentieth century shows the relative positions of several entrances to the Ouels mining area, but it is not fully georeferenced. Some mines have been reported in the south-western part of the map and the archaeological team would like to confirm these locations. To this end, a geophysical prospection campaign was organised, which included electrical resistivity tomography (ERT) and microgravimetric profiling over the area of interest. Several anomalies were identified. Two of them, in the north, are very likely to be related to voids (robbed area), since gravimetric and electrical anomalies are superimposed. Conversely, in the southern part, where microgravimetric anomalies occur, there are no electrical anomalies, but cavities could be electrically shielded by the overburden. An additional deeper ERT shows a new but small resistivity anomaly in the upper slope, outside the area preliminarily surveyed. Although not all of the gravimetric anomalies are confirmed by the ERT, the geophysics ultimately proved very effective in supporting at least some archaeological targets in the northern part of the prospect.

Engineering geophysical investigations using electrical resistivity tomography for groundwater exploration in the Bodaibo district of the Irkutsk region

Relevance. The need in technical groundwater exploration to construct a groundwater well for water supply of the rotation village of the mining and processing plant "Svetlovsky" in the Bodaibo district of the Irkutsk region. The electrical resistivity tomography is a common method for studying the upper part of a cross section and is widely used in mineral prospecting, geological mapping, engineering surveys, hydrological and environmental studies. The application of electrical resistivity tomography in these conditions will allow substantiating the location of hydrogeological wells and boreholes. Aim. Assessment of the geological and hydrogeological conditions of the area of work for the prospect of extracting groundwater for technical water supply for the needs of the rotational camp. Objects. Bedrocks, which are characterized by high resistance values and are aquicludes; permeable low-resistance zones that are water-bearing rocks. Methods. Ground-based geophysical surveys using electrical resistivity tomography; two-dimensional inversion of ERT data and their interpretation taking into account engineering and geological data of drilling and the GIS complex. As a result of the engineering and hydrogeological surveys performed using ground-based geophysical surveys by electrical resistivity tomography, it was established that the aquifer system of fissured rocks of the Imnyakh suite of the Proterozoic sediment complex (PR2-3im) is represented by fissured limestones of various colours from grey to blueish, with bands of mica schist. Analysis of the study results showed that the thickness of the exposed sediments is up to 50 m, the groundwater level of the operating horizon is opened at depths from 21 to 28 m. They are covered with a complex of low-permeability sediments of thickness from 5 to 11 m that are presented by interbedding of dense grey limestones and black metasandstones.

Joint inversion of ERT and ambient noise surface wave data with DPC-guided fuzzy c-means clustering for near-surface imaging

SUMMARY We present a novel strategy for performing joint inversion with guided fuzzy c-means (GFCM) clustering coupling and apply it to electrical resistivity tomography (ERT) and ambient noise surface wave (ANSW) data. To accurately extract a priori clustering information, we use density peak clustering (DPC) rather than fuzzy c-means (FCM). The number and centres of resistivity and shear-wave velocity a priori clusters are extracted by DPC and then used to guide the joint inversion with the GFCM clustering coupling of ERT and ANSW data. Synthetic and field data are used to evaluate the flow and algorithm of DPC-GFCM clustering joint inversion. The results of synthetic examples show that the models recovered by the DPC-GFCM clustering joint inversion are nearly the same as the true models and are more accurate than those inverted using individual inversion and FCM-GFCM clustering joint inversion. In the field case, the depths of the stratigraphic interfaces shown in the resistivity and shear-wave velocity models inverted by DPC-GFCM clustering joint inversion are nearly consistent with those from the drilling data. In contrast, the strata recovered by the individual inversion and FCM-GFCM clustering joint inversion significantly differ from the drilling results. Both the synthetic and field examples verify the effectiveness of the DPC-GFCM clustering coupling method used for the joint inversion of ERT and ANSW data acquired from the near surface with strong heterogeneity. This novel approach can also be applied to other types of geophysical data.

Magnetic and resistivity imaging of a probable fault within the Precambrian crystalline rocks in Ogbomoso, Southwestern Nigeria

A linear structure which is interpreted to be a fault was identified within the Precambrian basement complex rocks of the Ogbomoso Southwest Sheet 222 geological map, southwest Nigeria. The ground magnetic and electrical resistivity methods were used to investigate the structure and determine its physical characteristics. Five (5) traverses with lengths varying from 700–800 m and trending approximately NW–SE were established perpendicularly to the suspected fault. Total magnetic field data were acquired at 10 m interval, corrected for diurnal variation and inverted into 2D magnetic models using the Geosoft Oasis montaj software package. Dipole-Dipole resistivity data were acquired along the traverses using a dipole length of 20 m with expansion factor n varying from 1 to 5 and modelled to generate 2D resistivity structures with the DIPPROTM software package. Thirty-seven (37) depth sounding datasets were acquired, quantitatively interpreted and the results used to generate geoelectric sections across the suspected geologic feature. Three major magnetic dyke lineaments D1, D2 and D3 (60 – 164 m wide and 70 – ∞ depth extent) characterised by peak negative (−44 to −81 nT) magnetic anomalies and equivalent resistivity lineaments R1, R2 and R3 (50 – 140 m wide and 40 to >60 m depth extent) typified by low resistivity (10 – 750 Ωm) vertical discontinuities were delineated. The northern edges of lineaments D2 and R2 coincide significantly with the spatial location of the suspected fault F1 – F1 while D1 and R1 and D3 and R3 correlated and are newly identified parallel faults F2 – F2 and F3 – F3 to F1 – F1 and probably syngenetic with it.

Assessing an Abandoned Pyrite Cinder Deposit in Southeast Spain with Electrical Resistivity Tomography: A Case Study

Industrial activities have historically generated significant quantities of by-products, including pyrite cinders, a residue produced during the synthesis of sulphuric acid. This study presents a multidisciplinary approach to characterise an abandoned pyrite cinder deposit. Combining geophysical (electrical resistivity tomography—ERT), geochemical, and statistical methods, we assess the physicochemical properties of the deposit and its environmental implications. Our findings reveal the presence of heavy metals, with lead (7017.5 mg.kg−1) being the most concentrated element on the surface of the deposit, exceeding local legal thresholds by more than 163 times, posing environmental risks and inhibiting vegetation growth. Subsurface characterisation indicates a decreasing concentration trend of metals with depth, alongside variations in pH and electrical conductivity. Clustering analysis identifies groups of similar behaviours between resistivity, the most abundant heavy metals, and other variables, providing valuable insights into the complex interplay within the deposit. Our study underscores the importance of integrated approaches in assessing and managing hazardous waste sites, with implications for environmental remediation strategies.

Geofyzikální průzkum a datování sesuvu v údolí Javorné (Zlatohorská vrchovina)

The newly identified Javorná landslide (GPS 50.2506 N, 17.3099 E) is located above the Javorná settlement (Jeseník District, the Olomouc Region, Czechia) about 0.5 km southeast of Bílý kámen Mt. (612 m a. s. l.) within the Zlaté Hory Upland. The landslide was geomorphologically mapped, dated using the radiocarbon method, and geophysical measurements using electrical resistivity tomography were carried out to interpret surface and subsurface structure of the landslide. It is a rotational rockslide developed in deluvium formed by rocks of the envelope of the Desná Unit (orthoquartzites > amphibolites, gneisses), covering an area of approximately 0.11 km2 (~ 400 × 300 m). Up to three headscarps were identified, including the uppermost amphitheatre-like, which is discontinuous and not very prominent. The most significant scarp borders the landslide on the north-east all the way to its toe. Central part of the landslide is undulated, with several zones of local shallow depressions. The largest temporary water area (sap pond) documented in spring 2023 in the southern part of the landslide is ca. 10 × 5 m large. The toe of the landslide reaches in places the Javorná Stream, and it is possibly partially eroded. Frequent springs were noticed in front of the headscarp of the landslide. The resistivity profile through the landslide shows the maximal thickness of the landslide body to be 16 m in the lower part of the slope. The body of the landslide is characterized by the zone of higher resistivity values with sharp shear surface which is clearly visible from the resistivity data. Radiocarbon dating of the sedimentary fill of the intracolluvial depression determined the minimum age of the landslide to be 2760 to 3290 ± 30 years BP.

Deciphering of karst geomorphology and sinkhole (doline) structures using multiple geophysical and geological methods (Trabzon, NE Türkiye)

To date, in Türkiye only a limited number and volume of combined geophysical and geological studies about karst have been performed. In this study, karstification and geomorphological features were examined with geophysical and geological methods together and initial results were obtained for Türkiye. Although the geology of the limestone forming the Şahinkaya Member, which contains Çayırbağı, Çalköy, and Çal Cave, near the Düzköy district of Trabzon/Türkiye province was studied by many researchers to date, there is no geophysical study to determine the internal structural features, groundwater, dolines, and karstic voids. The aim of this study was to identify karst formations and their structural extensions in Şahinkaya Member with geophysical methods. Therefore, three different study locations with a total surface area of approximately 3.2 km2 were examined with electrical resistivity tomography, self-potential, seismic refraction tomography, multichannel analysis of surface waves, and ground penetrating radar. These geophysical applications in limestone helped to identify karst cavities, water-saturated zones and dolines. Finally, the order of priority and efficiency of the five applied geophysical methods was compared, and the stages of the applications were outlined. In addition, the origin of karstification in the area investigated in this study was supported by petrographic, petrophysical and rock mechanic data.

Research of electrical impedance tomography based on multilayer artificial neural network optimized by Hadamard product for human-chest models

Electrical impedance tomography (EIT) is a non-radiation, non-invasive visual diagnostic technique. In order to improve the imaging resolution and the removing artifacts capability of the reconstruction algorithms for electrical impedance imaging in human-chest models, the HMANN algorithm was proposed using the Hadamard product to optimize multilayer artificial neural networks (MANN). The reconstructed images of the HMANN algorithm were compared with those of the generalized vector sampled pattern matching (GVSPM) algorithm, truncated singular value decomposition (TSVD) algorithm, backpropagation (BP) neural network algorithm, and traditional MANN algorithm. The simulation results showed that the correlation coefficient of the reconstructed images obtained by the HMANN algorithm was increased by 17.30% in the circular cross-section models compared with the MANN algorithm. It was increased by 13.98% in the lung cross-section models. In the lung cross-section models, some of the correlation coefficients obtained by the HMANN algorithm would decrease. Nevertheless, the HMANN algorithm retained the image information of the MANN algorithm in all models, and the HMANN algorithm had fewer artifacts in the reconstructed images. The distinguishability between the objects and the background was better compared with the traditional MANN algorithm. The algorithm could improve the correlation coefficient of the reconstructed images, and effectively remove the artifacts, which provides a new direction to effectively improve the quality of the reconstructed images for EIT.

The “Annunziata” Garden in Cammarata (Sicily): Results of integrated geophysical investigations and first archaeological survey

A multi-method geophysical investigation was carried out in the context of a recovery project for the “Annunziata” Garden located in the town of Cammarata (Sicily), near to the homonymous church (Chiesa dell'Annunziata). In this area, according to the scarce historical sources, there was a Benedictine convent, probably demolished in the 18th century, but the area was probably inhabited even in earlier periods. Preliminarily, a series of 2D electrical resistivity tomographies (2D-ERT) were carried out approximately parallel to each other, some of which highlighted resistivity anomalies that could be attributed to buried archaeological structures. Consequently, in a smaller area where these anomalies were evident, a 3D electrical resistivity tomography (3D-ERT) and Ground Penetrating Radar (GPR) parallel profiles were carried out aimed at a detailed 3D reconstruction of the subsoil. Despite the unclear correspondence between the 3D-ERT inverse model and the GPR one, the 3D ERT confirmed the anomalies found with the previous 2D-ERT surveys, better defining its contours and geometries. The geophysical reconstructions served to indicate to the archaeologists the most promising areas for excavation tests that were carried out subsequently and confirmed the presence of archaeological structures, such as defensive walls whose origin and dating are still the subject of further archaeological studies.

Patterns of electrical properties change of heavy metal-organic compound contaminated media in soil-groundwater systems: From laboratory experiments to site application

Differences in electrical properties of media are the basis for determining the type and extent of contamination using geophysical methods. However, differences in heavy metals and organic matter complicate the electrical properties of compound-contaminated media, and existing geophysical methods cannot independently identify compound contamination. Therefore, this study proposes a geophysical detection system that combines electrical resistance tomography (ERT) and induced polarization methods and establishes a solid theory as the basis for the system application through laboratory experiments, model analysis, and site applications. The study reveals that as the organics volume proportion increases, the resistivity and normalized chargeability of contaminated media increased slowly, followed by a rapid increase, and finally reached a stable state. The specific type of compound significantly influences the electrical properties, while the resistivity of different kinds of compound-contaminated media reaches the same maximum value as the organics volume proportion increases. The medium type determines the contaminated media's lower resistivity limit and upper normalized chargeability limit. Additionally, the interplay between heavy metal type, content, and medium complicates the electrical properties of the media, with the compound type exerting a significant impact on resistivity. Archie's law and random forest modeling reveal that the inflection point for resistivity change occurs at 40 % and 80 % organics volume proportions, while the inflection point for normalized chargeability change occurs at 30 % and 70 % organics volume proportions in compound-contaminated media. These inflection points depend on the types of compounds, compositions, proportions, and media, and their importance for the electrical properties of the media changes with the increasing organics volume proportion. Based on the changing patterns of resistivity and normalized chargeability in heavy metal-organic compound contaminated media, the modified geophysical detection system can effectively identify the pollution type and intensity, which provides accurate pollution information to develop effective treatment strategies.

Characterizing spatial distribution of ice and methane hydrates in sediments using cross-hole electrical resistivity tomography

Electrical resistivity is an essential parameter for assessing the abundance of gas hydrates and predicting their location. However, imaging techniques are poorly developed for detecting the electrical resistivity distribution of hydrate-bearing sediments. In this study, a cross-hole electrical resistivity tomography (CHERT) array was established in the large-scale simulator for characterizing the spatial distribution of the sedimentary system. Ice- and methane hydrate-bearing sediments were investigated respectively using CHERT. The results show that CHERT effectively observed the significant influence of methane hydrate/ice formation and salt drainage on the variations in electrical parameters. Their formation leads to a sustained increase in average resistivity, while salt ion exclusion leads to an increase in pore water salinity, resulting in a decrease in local resistivity. Moreover, CHERT observed a range of resistivities from a few Ω·m to several thousand Ω·m for ice- and methane hydrate-bearing sediments, which is consistent with the resistivity response of hydrate reservoirs in the field. It is suggested that CHERT can be used for hydrate reservoir detection and combined with acoustic imaging to more accurately characterize the spatial distribution of hydrates. These results contribute to advancing the potential application of CHERT technology in multi-method and multi-scale gas hydrate monitoring initiatives.

Application Research of Integrated Geophysical Methods in Hydrogeological Survey in Extremely Arid Desert Areas

The research area is located in the Wuyi Mountain area of Dunhuang, Gansu Province, belonging to an extremely arid desert region. Previous hydrogeological surveys in the area had not conducted geophysical exploration work, and most of the hydrological boreholes previously drilled had either low water yield or almost no water yield. In this study, based on a comprehensive analysis of existing regional geological and hydrogeological data, the researchers conducted Controlled Source Audio-frequency Magnetotellurics (CSAMT) measurements and high-density electrical resistivity tomography (ERT) measurements. This work essentially identified the hydrogeological characteristics such as buried fracture water in the structural zones of the research area and water-rich properties. Hydrogeological boreholes were then deployed, and subsequent drilling confirmed a relatively high water yield.

Evaluation of injection current frequency on molten NaCl solidification images reconstructed by high-temperature electrical resistance tomography

Abstract The injection current frequency has been evaluated on molten NaCl solidification images reconstructed by high-temperature electrical resistance tomography (htERT). The evaluation was performed using an electrical equivalent circuit consisting of an electrical double layer (EDL), bulk solution and current–voltage path (CV path). The EDL and bulk solution are the elements that indicate electrochemical noise and bulk noise due to random thermally excited vibrations of Na+ and Cl–. The CV path compensates for measurement device errors due to the low resistivity of molten NaCl. The molten NaCl solidification images were reconstructed by htERT in an alumina crucible with platinum-wire electrodes under an initial temperature air T 0 = 820 °C and temperature drop rate γ = 6.67 °C min−1. As a result, the solid volume fraction φ of molten NaCl was properly obtained at the appropriate injection current frequency of L f < f < H f , which is determined by the electrical equivalent circuit (EEC) with an EDL, bulk solution and CV path. The EEC was validated by comparing the signal to noise ratio and Nyquist plot obtained experimentally with a resistance error. The best frequency range implemented in htERT for molten NaCl solidification images was determined as L f = 1.4 kHz and H f = 41 kHz.

The general patterns of water flow in loess slope system and implications for slope geological security

Loess regions face significant challenges in quantifying hydrological processes and assessing geological environmental risks due to the prevalent development of preferential pathways and the limitations of existing monitoring technologies. To advance this knowledge, this study presents an improved electrical resistivity tomography (ERT) device, specifically designed for loess moisture observations. By refining the testing principle, power supply mode, and data collection method within the existing ERT framework, the new device offers unmanned operation, automatic data acquisition, remote transmission, and cost efficiency. It effectively tracks water movement and groundwater level fluctuations across various hydrological conditions, supporting long-term online monitoring of hydrological processes of loess slopes. Through the analysis of monitoring data and classification of 12 observed preferential flow types, water movement in loess systems can be generalized into four general patterns: uniform infiltration, preferential infiltration, inflowing diffusion, and lateral flow. This generalized scheme provides a simplified modeling approach for other researchers to quantify slope hydrodynamics and to assess geological safety risks involving preferential flow. Based on these insights and field investigations, a conceptual framework is proposed to elucidate the seepage-structure synergistic initiating mechanism of loess landslides. This framework suggests that water entry and movement patterns within the slope depend on the slope geological structure related to preferential pathways and the prevailing hydrological scenarios. Landslide occurs as the result of the progressive failure and reciprocal evolution between the slope hydrological environments and geological structure, which may also pose potential eco-hydrological risks. The outcome advances the development of slope hydrological monitoring technology and enhances the understanding of water movement laws and the associated geological environmental risks in loess slope systems, which is of vital importance to the early warning methods of loess landslides that account for preferential flow and for theoretical modeling of preferential flow in related disciplines.

3D Effect and countermeasure of 2D geoelectrical imaging of a subsurface linear structure

This study was prompted by a field observation of a resistivity anomaly in a 2D Electrical Resistivity Tomography (ERT) scan during a fault investigation, suspected to be an artifact from an unnoticed 3D effect. Numerical simulations explored potential 3D effects when the survey line is not perpendicular to the strike of a linear feature, violating the ideal 2D assumption. Artifacts similar to the observed field anomaly arise when the survey line is oriented at an angle <60° from the strike. This 3D effect pattern, resulting from an oblique survey line, is quite different from the known mirroring effect of off-plane objects. Previously overlooked in practical applications, this phenomenon could lead to misinterpretations. A comprehensive investigation considering various influencing factors clarified the conditions and behaviors associated with this 3D effect. Further numerical studies of pseudo-3D surveys propose a practical guideline to avoid this effect with minimal effort. When field conditions raise concerns about surveying at an acute angle to the strike, adding one more survey line on each side of the main survey line, offset by two electrode spacings, is recommended. The 3D inversion of this narrow 3-line pseudo-3D survey can accurately resolve the in-line resistivity section.

Geoelectrical characterization of non-filled active faults in Jaral de Berrios, Guanajuato, México

Electromagnetic and electrical methods have a great number of applications and have become a commonly used tool for the study of active geological faults, where they are usually detected as low resistivity anomalies. However, this is not always the case. We used both Electromagnetic Profiling (EMP) and Electrical Resistivity Tomography (ERT) methods with the aim of mapping active geological faults which affect agricultural plots and a former quarry near the town of Jaral de Berrios, State of Guanajuato. The apparent resistivity map derived from EMP survey shows how NW-SE on site measured faults (which reach at least 400 m in length and 0.4 m in width) match with high apparent resistivity anomalies. Two ERT profiles reveal the subsurface continuity of the main fault zones, as well as the main high apparent resistivity lineaments, for at least 40 m below the surface. The resistive lineaments in the apparent resistivity map showed a coincidence with the faults modeled in the geoelectric section of the ERT1 profile; this result gives reliability to the methodology used in the study site. All of this means that faulting presently evident on the surface continues at depth and has a wider extension than previously thought, and that since the fractures are non-filled with minerals and/or moisture the preponderance of high resistivity anomalies make sense. The results of this work provide the basis for future studies that help in determining the type of faulting affecting our study area, so long term urban planning and development in the area may be possible.

Integration of ground geophysical methods to characterize near‐surface aquifer zones within an active mine

AbstractUnderstanding near‐surface groundwater storage, flow patterns, surface and groundwater interactions in mining areas can assist in making mining more efficient and profitable. This is especially important in opencast mines affected by water inflows that may negatively affect production and increase mining costs. We map and characterize the near‐surface aquifer zones at the opencast site of Tharisa Minerals, located in the southwestern region of the Bushveld Complex (South Africa). The main goal is to infer pit water inflow at the mine site and determine how it may be better controlled. The Bushveld Complex hosts partially connected and unconfined alluvial, shallow‐weathered and crystalline bedrock aquifers, which are often connected by small‐scale permeable zones. Seismic refraction tomography, multichannel analysis of surface waves, electrical resistivity tomography and borehole data are used to map and understand the different aquifer zones in the vicinity of the mine, as well as infer their relation to water inflow in the mine pits. The geophysical surveys map the overburden, weathered bedrock aquifer zone, and the top of the crystalline aquifer rock zone reasonably well. They reveal extensive and deep weathering, and possible high hydraulic conductivity in the vicinity of the mine. The results provide a better understanding of the mine's near‐surface environment, which could be used to implement effective and targeted dewatering techniques, thus enabling better pit inflow water control to improve mine working conditions and production.

Observations of electrical resistivity tomography and groundwater level under an irrigated terraced paddy field in northern Taiwan

Observations of electrical resistivity tomography and groundwater level under an irrigated terraced paddy field in northern Taiwan

Intelligent geological interpretation of AMT data based on machine learning

AMT (Audio Magnetotelluric) is widely used for obtaining geological settings related to sandstone-type Uranium deposits, such as the range of buried sand body and the top boundary of baserock. However, these geological settings are hard to interpret via survey sections without conducting geological interpretation, which highly relies on experience and cognition. On the other hand, with the development of 3D technology, artificial geological interpretation shows low efficiency and reliability. In this paper, a machine learning model constructed using U-net was used for the geological interpretation of AMT data in the Naren-Yihegaole area. To train the model, a training dataset was built based on simulated data from random models. The issue of insufficient data samples has been addressed. In the prediction stage, sand bodies and baserock were delineated from the inversion resistivity images. The comparison between two interpretations, one by machine learning method, showed high consistency with the artificial one, but with better time-saving. It indicates that this technology is more individualized and effective than the traditional way.