Electrical Resistivity Tomography Method Research Articles

Application of electrical resistivity tomography and geotechnical techniques for identification and characterization of collapsible soils in Bafoussam (Western, Cameroon)

Road failure catastrophes have increased in frequency in the West Cameroon area. The collapsed soil characteristics that contribute to these phenomena in Bafoussam have been investigated using the geophysical investigation combined with geotechnical tests. The result of electrical resistivity tomography shows water conditions and heterogeneity of road foundation materials: resistivity values higher than 200 Ωm indicate dry materials, values between 30 and 200 Ωm define wet materials, and values lower than 30 Ωm indicate the very wet or water-saturated materials. These water-saturated materials can therefore move, bounded by a sliding surface of high-resistivity materials. Geotechnical properties analysis shows that these materials are clayey-sensitive water (64% clay fraction; A-7-6), very plastic (liquid limit: 46–63% plasticity limit: 29–39%), compressible, with high porosity (e > 0.8), low shear strength, and high friction angle (24–37°). The quality of foundation materials associated with high slopes (> 40°) and heavy rainfall in wet seasons (July–October) means that seepage water is the main factor responsible for the mass movement observed on the road of Western Cameroon. The construction or rehabilitation of these roads should be carried out in compliance with the natural conditions of the project site.Article highlights- 2D Electrical Resistivity Tomography method is able to determine the nature, subsurface structure and water conditions of road foundation soils.- Geotechnical test can be used to define the physical and mechanical properties of road foundation soils.- These two techniques complement each other to understand the mass movement observed on two sections of road failures caused by seepage water.

Landslide ground model development through integrated geoelectrical and seismic imaging in Thungsong district, Nakhon Si Thammarat, Thailand

A ground model of a shallow landslide in rainfall-induced slope failure of Thungsong, Nakhon Si Thammarat, southern Thailand is developed through an integrated geophysical approach, utilising electrical resistivity tomography and P-wave seismic refraction tomography (SRT) methods. Those two methods were applied to assess landslide structure and study deformation mechanisms along four profiles. Beside the four profiles there is another profile, which was acquired near an borehole and used for the calibration with geological data. Our results show subsurface structures in terms of the ground model used to determine stratigraphic layers, zones of saturation or groundwater table, and significant differences between the landslide slip material and the underlying bedrock. The clay-rich zones (resistivity less than 500 Ωm) in the colluvium on the relatively steep slope, show enhanced potential for landslides. This silty clay plays an important role for landslide activation in this site. Moreover, a combination of steep slopes, shallow basement rocks overlain by clay-rich colluvium, and seasonally high rain fall leads to landslides in the region. The ground model produced by geophysical imaging for this region achieves a comprehensive understanding of the structure and lithology of a complex landslide system and overcomes the limitations of remote-sensing data or isolated intrusive sampling techniques alone.

Electrical resistivity tomography through reinforced concrete floor

AbstractThe electrical resistivity tomography (ERT) method is often challenged by the presence of reinforced concrete (RC) in urban and industrial environments, because the embedded metallic wire mesh can severely distort the distribution of subsurface currents. We investigate one typical scenario in real applications, in which an RC floor overlays the natural topsoil or rock. Our synthetic forward simulations show that the embedded wire mesh behaves like a local good conductor in data of small source‐receiver separations and acts like an equal‐potential object that keeps the potential from decaying at large source‐receiver separations. Routine ERT inversions that ignore the RC cannot work properly because the thin and highly conductive wire mesh may be manifested as large uninterpretable low‐resistivity anomalies in the imaging results. Two remedies are adopted to improve the ERT resolution in such cases. First, we find a top layer with high conductivity in our model to adequately represent the wire mesh; then, we initiate the inversion with the top‐layer model as the starting and reference model. This warm‐start approach overcomes the difficulty of recovering the large conductivity contrast between metallic objects and regular earth materials. Second, underground electrodes are added to the survey array, so more information from depth can be obtained to fight against the dominance of current channelling in the wire mesh. Finally, our strategies are used to invert a real ERT dataset from an indoor manufacturing plant, where RC covers the entire floor of the building and electrodes are in contact with the soil through open holes in the floor. Our simulation and field data inversion verify our findings and demonstrate the effectiveness of our solutions in improving the resolution of ERT when the survey is carried out over RC floor in urban and industrial environments.

New Insights from Geophysical, Hydrogeological and Borehole Data into the Deep Structure of the Louta Phosphatic Deposit (Gantour Basin, Morocco): Mining Implications

The Gantour Phosphatic Basin (GPB) is formed by a sedimentary series of Maastrichtian to the Eocene age, which consists of alternating phosphate layers and sterile levels. This series outcrops in the northern part of the basin, where it is exploited in open-pit mines. The exploration methodology employed by the Office Chérifien des Phosphates (OCP) group to investigate the GPB is based on direct recognition with boreholes drilled on a 500 × 500 m grid. This research is concerned with the compilation and analysis of data collected during several drilling campaigns conducted on the central segment of the GPB, namely the Louta deposit. This research also includes acquiring, processing, and interpreting new geophysical and hydrogeological data. Its main objective is to provide a better understanding of the deep structure of the phosphatic series. Therefore, the present study was carried out according to a multidisciplinary approach that comprises three parts. (i) The first one involves geological modeling of the exploration borehole data using Datamine Studio RM software (version 1.4), developed by Datamine Corporate Ltd., (Bristol, United Kingdom). It results in establishing a series of geological cross-sections that display a detailed view of the deep structure of the phosphatic series and its lateral variations. (ii) The second part is related to the hydrogeological study, whose purpose was to elaborate on an accurate and updated piezometric map of the study area. The new map helps understand the groundwater flow in the Louta deposit. Furthermore, the superimposition of the piezometric level with the geological sections throws light on the flooded volume of phosphate in this deposit. (iii) The third part of the study focuses on implementing the Electrical Resistivity Tomography (ERT) method. The interpretation of the recorded geoelectrical data not only highlights the main features controlling the mode and the proportion of the phosphate series deepening under the Plio-Quaternary cover but also confirms the evolution of the overall structure of the studied area. The obtained 2D ERT models generally corroborate the cross-sections produced by geological modeling. They also correlate with the information provided by the hydrogeological study. Such information will help guide future hydrogeological and mining extraction planning in the studied area.

Geophysical and Geochemical Pilot Study to Characterize the Dam Foundation Rock and Source of Seepage in Part of Pensacola Dam in Oklahoma

Pensacola Dam, operated by the Grand River Dam Authority (GRDA), is a multiple-arch buttress dam constructed in 1940. The dam has little or no existing geophysical reports on the integrity of the dam foundation rock and even less knowledge at depth. Visual inspection indicated evidence of seepage at some arches of the dam. As a pilot study, we conducted a suite of geophysical surveys inside two arches (Arch-16 and Arch-17) and a part of the downstream berm to characterize the dam foundation rock, delineate seepage zones, and identify the most appropriate geophysical methods for temporal monitoring of the dam’s conditions. The geophysical methods included electrical resistivity tomography (ERT), self-potential (SP), multichannel analysis of surface waves (MASW), compressional (P)-wave refraction, and shear (S)-wave reflection. Water samples were collected for geochemical analysis to investigate the source of the seepage flow inside Arch-16. The geophysical results characterized the dam foundation rock into an unsaturated limestone and chert overlying a water-saturated limestone and chert. The ERT profiles indicated that groundwater is rising inside the arches and significantly dropping under the downstream berm, which can be due to the uplift pressure beneath the dam base. Zones of high seepage potential were detected near the buttress walls of the two surveyed arches, which may be related to previous blasting, excavation of the dam foundation, concrete placement, or improper grouting. The geochemical analysis of water samples taken from the artesian wells inside Arch-16 and the Grand Lake revealed different chemical compositions, suggesting that the source of water could be a mixture of groundwater and lake water or lake water interacting with rock and reaching the surface through fractures; however, more sampling and further analysis are required to ascertain the source of the seeps. This study showed that the ERT, SP, and S-wave reflection methods have effectively characterized the dam foundation rock and seepage zones beneath the arches. The study provided a better understanding of the conditions of the dam foundation rock, evaluated the utilized geophysical methods, and determined the optimum geophysical methods that can be used for the characterization and monitoring of the subsurface conditions along the entire length of the dam. In this study, we have demonstrated that the integration of effective geophysical surveys and geochemical analysis yielded optimum results in solving a complex dam safety problem. This strategy promotes the best practice for dam safety investigation.

Using Electrical Resistivity Tomography Method to Determine the Inner 3D Geometry and the Main Runoff Directions of the Large Active Landslide of Pie de Cuesta in the Vítor Valley (Peru)

Pie de Cuesta is a large landslide with a planar area of 1 km2 located in the Vítor district, in the Arequipa department (Peru), and constitutes an active phenomenon. It belongs to the rotational/translational type, which concerns cases that are very susceptible to reactivation because any change in the water content or removal of the lower part can lead to a new instability. In this context, a previous geological study has been decisive in recognizing the lithologies present and understanding their behavior when they are saturated. But it is also necessary to know the inner “landslide geometry” in order to gusset a geotechnical diagnosis. The present study shows how the deep electrical profiles (ERT, electrical resistivity tomography method), supported by two Vp seismic refraction tomography lines (SVP), have been used to create a 3D cognitive model that would allow the identification of the inner landslide structure: the 3D rupture surface, the volume of the sliding mass infiltration sectors or fractures, and the preferred runoff directions. Moreover, on large landsides, placing the geophysical profiles is a crucial aspect because it greatly depends on the accessibility of the area and the availability of the physical space required. In our case, we need to extend profiles up to 1100 m long in order to obtain data at greater depths since this landslide is approximately 200 m tall. Based on the geophysical results and geologic information, the 3D final model of the inner structure of this landslide is presented. Additionally, the main runoff water directions and the volume of 90.5 Hm3 of the sliding mass are also estimated.

Lithology Of Geothermal Potential Areas Using The Electrical Resistivity Tomography (ERT) Method

The rock lithology of the potential hydrothermal area has been studied using Electrical Resistivity Tomography (ERT) in Pungguk Pedaro Village, Bingin Kuning District, Lebong Regency. Field data acquisition uses a stretch length of 480 meters with the MAE X612-EM Geoelectric tool that forms a straight line. ERT method, using Res2dinvx64 software. This study aims to determine the subsurface conditions of the potential hydrothermal area and the characteristics of the rocks that make up the hydrothermal area. The results of this study can be concluded that Pungguk Pedaro Village is dominated by Clay, Sandstone, Sandy Gravel, Andesite, Basalt, and Granite rocks. Line 1 has no potential for hydrothermal distribution because there has been a mixture of hydrothermal water with mountain water, so only groundwater is obtained on this line.

DETERMINATION OF OPTIMAL OBSERVATION NETWORK PARAMETERS FOR MAPPING PALEOCHANNEL BY THE ELECTRICAL RESISTIVITY TOMOGRAPHY METHOD BASED ON NUMERICAL AND PHYSICAL MODELING

Link for citation: Osipova P.S., Olenchenko V.V., Chekryzhov A.V. Determination of optimal observation network parameters for mapping paleochannel by the electrical resistivity tomography method based on numerical and physical modeling. Bulletin of the Tomsk Polytechnic University. Geo Аssets Engineering, 2023, vol. 334, no. 10, рр. 232-242. In Rus. The relevance of the study is explained by the need to determine the methodological features of applying the electrical resistivity tomography method to map paleochannels when prospecting for placer gold. The main aim: to determine the necessary and enough parameters of the observation network for paleochannel mapping based on numerical and physical modeling. Object: electrical fields on the physical and numerical model of the paleochannel. Methods: electrical resistivity tomography, physical experiment, numerical simulation. Results. Electrical soundings by electrical tomography were carried out on a physical model of a river valley. In addition, a numerical experiment was performed on a three-dimensional model of a river valley fragment with a paleochannel. The unit of the survey scale is the distance between two electrodes, which in the experiment is 1 cm and is equivalent to 5 m in real field studies. The distance between the profiles varied from 2 to 12 cm with a step of 2 cm, which corresponds to different survey scales. In accordance with geological concepts, the authors formed a model of a river valley with a segmentally gently stage of channel formation. Three-dimensional inversion was carried out for the data set obtained at the maximum density of the observation network, and then for the data sparse to the desired scale. On the resistivity map, the paleochannel is recognized by a ribbon-shaped high-resistivity anomaly. The analysis of the maps showed that to determine the shape of the paleochannel in plan, it is necessary to use the observation network scale of 1:3000, at which the distance between the profiles is 30 m. The physical experiment results were confirmed by mathematical modeling. The scale should be reduced to 1:5000 with detailing in individual areas to improve the economic efficiency of geophysical research.

Reducing the risk of missing soil contamination by integrating multi-investigated methods in a retired chrome salt factory

An effective contamination screening process is essential for mitigating the risk of overlooking pollution during site investigations. While Electrical resistivity tomography (ERT) and portable X-ray Fluorescence (XRF) offer quick assessments of contaminated areas, there is a notable gap in research regarding ERT’s application in the unsaturated soil layer, and portable XRF’s use for screening polluted samples in chromium-contaminated sites. This study gathered soil pollution and electrical resistivity data from a decommissioned chrome salt factory, employing drilling, sampling, XRF, and ERT methods. Predominantly, sulfate and chromium emerged as the pollutants, with concentrations ranging from 19.24 to 12700.00 mg/kg for sulfate, 0.65 to 3000.00 mg/kg for Cr(VI), and 12.00 to 27800.00 mg/kg for total Cr, respectively. Polluted hotspots were identified by lower apparent soil resistivity compared to the background levels at corresponding depth. Notably, a significant inverse correlation was observed between sulfate and Cr(VI) concentration and soil resistivity, particularly with sulfate (R2 =0.48) demonstrated through a power function fit at depths ranging from −4 to 0 m. The XRF analysis for total Cr concentration exhibited a significant correlation (Pearson’s r = 0.67) with chemical analysis, confirming 1000 mg/kg as an effective screening threshold. In light of these findings, this study proposes a scientific procedure that integrates drilling, sampling, ERT, and XRF for soil contamination investigation. This framework aims to support similar site assessments, reducing the risk of overlooking contamination.

Geophysical investigation of pavement failure along Jonathan by-pass - Akansoko and Atimbo - Parliamentary roads in Calabar Metropolis Cross River State, Nigeria

This study examined pavement failure in some roads in Calabar Metropolis using electrical resistivity tomography method. Seven (7) measurements were taken at the natural soil opposite the failed and stable segments of the road with the aid of Wenner electrode configuration at spacing of 5.0, 10.0, 15.0, 20.0, 25.0, 30.0 and 35.0m with spread length of 105m. The findings of this study revealed that along Jonathan by- pass – Lafarge – Akansoko road, low resistivity values were 8.0Ωm – 73.0Ωm at Akansoko a stable segment; 6.0Ωm - 17.0Ωm at Ukwua Itiat and 30.0Ωm - 94.0Ωm at Idundu market a failed segment. Along Atimbo - Jonathan – Parliamentary road, moderate/high electrical resistivity values in the range 331.0 Ωm – 1018.0 Ωm across the profile was obtained at Federal Government Girls’ College by airport a control segment; 26.0 Ωm – 68.0 Ωm at opposite rice seedling site a failed segment and 49.0 Ωm – 74.0 Ωm at Message point Assembly Church. These results showed that the remote cause of road failure in the area is clay/shale/weathered geologic materials with low resistivity values. It was recommended that detailed geophysical investigation should always be conducted on any proposed site for road construction and/or rehabilitation before embarking on the project.

Geophysical Research on an Open Pit Mine for Geotechnical Planning and Future Land Reclamation: A Case Study from NW Macedonia, Greece

In open pit mining areas, knowledge of geotechnical conditions (e.g., overburden thickness, background slope, and fault locations) ensures geotechnical safety during exploitation as well as reclamation planning. The Greek Public Power Corporation initiated a research program after stability issues emerged on the southern side of the Mavropigi open pit mine in NW Macedonia. Geotechnical wells revealed steeply dipping bedrock and thin tectonic contact, indicating the need for the detailed imaging of the subsurface for future stability measures. For this purpose, a geophysical investigation aimed to extract information mostly for the dip of the interface between schist bedrock and overlaying Neogene sediments and/or limestones. Based on the high contrast of electrical properties between schists and limestones, as well as the differences in acoustic impedance and formation thickness, the seismic reflection and electrical resistivity tomography (ERT) methods were selected. The suitability of the seismic reflection for its application in this area was checked by generating synthetic seismic data, which resulted from the simulation of seismic wave propagation for geological models of the area. The acquisition parameters were determined after the noise test. Field seismic data processing produced a depth-migrated section, which revealed the existence of a fault. The use of dipole–dipole and gradient arrays, in 2D and 3D electrical resistivity measurements, ensured both the lateral and vertical mapping of schist bedrock and detected limestone bodies within the overburden. Also, the tectonic contact zone between limestone and schist formations was properly imaged. The comparison between geoelectrical and seismic sections indicated that the seismic reflection method provided a more accurate estimate of fault inclination. Finally, the geophysical survey enriched the geotechnical models necessary for sustainable mining (e.g., rational exploitation, the optimization of productivity, and zero accidents) including the planning of future reclamation.

Мониторинговые электротомографические исследования зоны Иссык-Атинского разлома (Северный Тянь-Шань)

In 2023, monitoring geophysical studies were carried out using the electrical resistivity tomography (ERT) method along three profiles that cross the strike zone of the Issyk-Ata fault in the transverse direction. A detailed study was carried out of the observed variations in apparent electrical resistivity, which characterize the change in the electrical properties of the upper part of the Earth's crust section with a 40-minute discretization in time. Using the analysis of difference pseudo-sections of apparent resistivity, constructed based on the results of ERT monitoring, the most informative pseudo-depth interval from the point of view of geoelectric activity was determined for all three monitoring profiles. Accordingly, for a pseudo-depth of 24 m on each monitoring profile, an assessment was made of the geodynamic activity of these sections of the Issyk-Ata fault based on an analysis of the magnitude of two parameters: the amplitude of apparent resistivity variations and the correlation coefficient of electrical resistivity variations with lunar-solar solid tides. High values of these parameters, in our opinion, determine the location of modern active fault zones.

Comparison of different inversion strategies for electrical impedance tomography (EIT) measurements

SUMMARY Electrical impedance tomography (EIT) is a promising method to image the frequency-dependent complex electrical conductivity distribution of the subsurface in the mHz to kHz frequency range. In contrast to the well-developed electrical resistivity tomography (ERT) method, the inversion approach for EIT data is less established. Different inversion strategies have been proposed, but the implications of the differences between these methods have not been investigated yet. In this study, we aim to compare four different inversion strategies for EIT measurements. The first strategy (CVI) formulates the inverse problem in the complex number domain and is mathematically the most elegant method. The second strategy (RVI) is the established real-valued inversion method, which decouples the inversion of the real and imaginary parts and completely ignores the complex nature. The third strategy (ALT) is very similar to the RVI strategy in case of small phase angles, but it considers the complex coupling in the forward operator and alternately updates the real and imaginary parts of the model in the case of large phase angles. The fourth and final strategy (CVI+) was newly formulated in this study. It fully considers the complex nature of EIT measurements but separates the treatment of the real and imaginary part in terms of the data weighting and regularization. The different inversion strategies were tested with two synthetic models. The first model has a small phase contrast and the second model has a large phase contrast. In the case of a small phase contrast, the CVI strategy was able to resolve the distribution of electrical conductivity amplitude, but the inversion result for the phase angle was less reliable. The other three strategies presented similar results and the models were well resolved within the expected data misfit. In the case of a model with large phase contrast, only the newly formulated CVI + strategy was able to produce reliable results. It was found that the extremely large phase angle can have a significant influence on the modelled amplitude of data. The cross-sensitivity (i.e. the imaginary part of the sensitivity) that describes the influence on the real part of data due to a change in the imaginary part of model, or that on the imaginary part of data due to a change in the real part of model, provided unique information during the inversion. It was concluded that the CVI + strategy is theoretically the most comprehensive and correct approach for EIT inversion, but that in the case of small phase angles the RVI strategy has the practical advantage that no complex calculations are required, which substantially reduces the required computational effort.

A New Method for Electrical Impedance Tomography With Incomplete Electrode Array

A New Method for Electrical Impedance Tomography With Incomplete Electrode Array

Cross-street electrical resistivity imaging for environmental applications

Road collapse has always been an important safety hazard for urban traffic, causing a serious threat to the safety of passing vehicles and citizens. However, the complex urban surface environment with obstacles such as huge buildings, hardened roads, and river network limits the application of ERT in cities. Here we present an innovative cross-street electrical resistivity imaging method. This method abandons the mandatory electrode grid layout that conventional 3D ERT required. Only two survey lines are required to be laid along sides of the street parallelly, gathering the apparent resistivity data set by the combination of current supply and potential electrodes across the street and obtaining the 3D resistivity imaging under street. It is well suitable for detecting and monitoring of hardened road and enhances the feasibility and the adaptability of ERT in urban. A series of numerical models and comparisons among this method and conventional ERT had been done. The modeling results show that this cross-street method reaches the resolution of the conventional 5-lines ERT, and its resolution to objects cross road are better than the conventional ERT. This method can both satisfy the exploration needs with difficult surface conditions such as roads, and greatly reduce the exploration workload. It shows well application prospects, such as hidden geological problem monitoring while combining with time-lapse ERT instruments.

Structural similarity driven joint reconstruction of conductivity and sound speed in EIT/UTT dual-modality tomography

A multi-parameter joint reconstruction method is proposed for electrical impedance tomography (EIT) and ultrasonic transmission tomography (UTT) dual-modality tomography based on statistical joint inversion framework. The inherent correlation of two imaging modalities is that the conductivity and sound speed parameters share the same structure, which can be defined by the structural similarity of the spatial distributions of conductivity and sound speed. The structural similarity between conductivity and sound speed is quantitatively characterized by a joint prior model with total variation and cross-gradient functionals. The multi-parameter joint reconstruction problem is constructed by Bayesian joint inverse model, and solved by maximum a posterior method with alternate solution strategy. Numerical and experimental tests are carried out to evaluate the performance of the proposed method. The results show that the proposed EIT/UTT dual-modality tomography method with structural similarity promoting can improve the reconstruction accuracy of conductivity and sound speed compared with the traditional single-modality EIT and UTT methods.

Maximizing RDF recovery potential through the integration of electrical resistivity tomography and frequency-domain electromagnetic surveys for waste characterization in open dump mining

Open dumping is a widespread waste management technique used in developing countries. This approach is simple and economical but has numerous environmental and health impacts. Open dump mining (ODM) can reduce waste in both open and controlled dumpsites by converting waste into refuse-derived fuel (RDF) for energy generation; however, before ODM implementation, the waste's characteristics and composition must be assessed. Geophysical surveys are widely used to characterize waste. The electrical resistivity tomography (ERT) method is a particularly common technique for determining waste composition, but it has several limitations. Therefore, a frequency-domain electromagnetic (FDEM) survey was used in this study as a pre-screening tool to evaluate the waste composition and overcome the limitations of ERT surveys. This study aimed to determine the relationship between geophysical data types (i.e., ERT and FDEM) and the optimal waste composition for RDF production and assess the ability of FDEM surveys to identify areas with RDF recovery potential. This study combined ERT and FDEM surveys with waste sample analysis in old/new controlled dumpsites in Thailand. The quantitative and qualitative correlations between the geophysical data (i.e., resistivity, conductivity, waste composition, and moisture content (MC)) were then assessed using linear and multiple linear regression analysis. Integrating geophysical surveys was found to have the potential to locate optimal RDF recovery areas, with low conductivity (0–100 mS/m) and high resistivity (>55 Ω·m) characteristics associated with areas of high RDF content (>40 % by weight). An unexpected finding was that increased waste age resulted in increased resistivity and decreased conductivity. Additionally, the MC depended on factors affecting spatial variability (e.g., precipitation and biodegradation). Overall, this study demonstrates that integrating ERT and FDEM surveys is a suitable pre-screening tool to evaluate waste characteristics and composition, mitigate ERT survey limitations, and improve waste investigation before ODM.

Frequency domain electromagnetic calibration for improved detection of sand intrusions in river embankments

Sand intrusions pose significant risks to river embankments due to potential flow pathways that can lead to instability during flood events. Visual inspection is a first step to recognize critical segments, but it does not deliver information about the subsurface. In this context, the electromagnetic induction (EMI) technique is a useful method for preliminary zoning at regional scale while the electrical resistivity tomography (ERT) method, widely used for hydrological purposes, is considered among the most reliable techniques for local subsurface imaging. A major sand intrusion within the levees of the Brenta River, located near Venice (northern Italy), resulted in water seeping during seasonal floods and posed severe threats to embankment stability. ERT and EMI techniques, along with geotechnical investigations, were the best survey choices to address the problem. Resistivity profiling successfully imaged the sand body geometry within and underneath the levee, and results correlated nicely with borehole stratigraphy. A first multiarray EMI device, which represented a faster and less expensive survey, was deployed to map further anomalies along nearby levees, but results were not satisfactory because the inverted profile failed to image the known intrusion. A second multiarray EMI device, with larger coil spacing, was also tested. Although it performed better in detecting the intrusion, results were still below expectations. A calibration procedure based on Pearson's coefficients and using ERT as a reference was then devised and implemented to correct the EMI data prior to carrying out inversion. The procedure was successful for both EMI data sets, leading to realistic subsurface resistivity in the inverted sections. EMI measurements could then be recovered and interpreted correctly to estimate subsurface textures. The possibility of calibrating EMI data and obtaining subsurface resistivity images comparable to standard ERT profiling is an important improvement for cost-effective EMI surveying of river embankments to mitigate flood hazards.

Integration of Ground Penetrating Radar and Electrical Resistivity Methods to Investigate Subsurface Features at Kish Archaeological site, Babylon, Iraq

Several geophysical techniques, including magnetic, Electrical Resistivity Imaging (ERI), and Ground Penetrating Radar (GPR), have been used to investigate archaeological features because they are non-destructive and inexpensive compared to traditional methods such as excavation. GPR has been used in the Governorate of Babylon, Kish archeological site to investigate the subsurface ancient features.The GPR survey carried out on three parallel profiles. The length of each profile is 29 m and the spacing between each adjacent profile is 15 meters. The antennas 450 MHz and 750 MHz were used. The data was processed using GPR SliceV7 software. The GPR profiles indicate the presence of buried features, which may be an ancient wall. The wall is buried at a depth range between 0.5 and 3 m. Outside the study area, some part of the wall is visible on the surface. Three Electrical resistivity image (ERI) profiles (1, 2 and 3) were carried out by using wenner array to check the main features detected by GPR method. The ERI results are confirmed the GPR profiles (1, 2, and 3). Both methods indicate the existence of an ancient wall trending NW-SE. The thickness of the wall is approximately 3m and is located at distance 7.5-10.5 meters at profile 1 in the south and at distance 10-13 m in profiles 2 and 3. The depth of the wall ranges from 3–3.5 m. Another deep wall was also detected in the GPR profile 1 and in the three profiles of ERI method. The current work confirmed the importance of using ERI method with GPR method to investigate shallow subsurface features.

Temporal and spatial distribution patterns of upper saline plumes and seawater-groundwater exchange under tidal effect

Under tidal influence, an active exchange process occurs between seawater and groundwater in the coastal aquifer system. However, in-situ studies and research on the temporal and spatial distribution patterns of upper saline plumes (USPs) and seawater-groundwater exchange process are lacking. In this study, we selected the Shilaoren beach in Qingdao as the study area, and used pseudo-3D electrical resistivity tomography (ERT) and hydrogeological measurement methods to monitor the spatial distribution of groundwater salinity and the seawater and groundwater exchange process. We found that during the ebbing tide, USPs were divided into several smaller USPs driven by groundwater discharge. Subsequently, during the flooding tide, high-salinity seawater recharge was observed, and several smaller USPs gradually aggregated into a complete USP. In coastal aquifers, the exchange of seawater and groundwater not only occurs through the beach surface and seepage face, but also includes high-permeability underground channels. Seawater and groundwater exchange occurs more rapidly through these underground channels randomly distributed at depth, which also leads to spatial differences in the seawater and groundwater exchange process. Additionally, affected by underground channels, the groundwater discharge flux shows spatial heterogeneity. In areas with underground channels, the groundwater discharge flux significantly increases. Therefore, the non-seepage face area has a similar groundwater discharge flux to the main groundwater discharge area, namely, the seepage face. In the intertidal zone of the study area (70 × 60 m), the total groundwater discharge flux through the seepage face is 3407.6 m3, and no significant difference is observed in the groundwater discharge flux at various parts of the seepage face. In the non-seepage face area, the groundwater discharge is highly spatially heterogeneous; the total groundwater discharge flux is 3252.0 m3, and approximately 60% of this occurs through densely developed underground channels.