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Forest cover has a significant effect on hillslope hydrological processes through its influence on the water balance and flow paths. However, knowledge of how spatial patterns of forest plots control hillslope hydrological dynamics is still poor. The aim of this study was to examine the impact of an across-slope forest strip on sub-surface soil moisture and groundwater dynamics, to give insights into how the structure and orientation of forest cover influences hillslope hydrology. Soil moisture and groundwater dynamics were compared on two transects spanning the same elevation on a 9° hillslope in a temperate UK upland catchment. One transect was located on improved grassland; the other was also on improved grassland but included a 14 m wide strip of 27-year-old mixed forest. Sub-surface moisture dynamics were investigated upslope, underneath and downslope of the forest over 2 years at seasonal and rainfall event timescales. Continuous data from point-based soil moisture sensors and piezometers installed at 0.15, 0.6 and 2.5 m depth were combined with seasonal (~bi-monthly) time-lapse electrical resistivity tomography (ERT) surveys. Significant differences were identified in sub-surface moisture dynamics underneath the forest strip over seasonal timescales: drying of the forest soils was greater, and extended deeper and for longer into the autumn compared to the adjacent grassland soils. Water table levels were also persistently lower in the forest and the forest soils responded less frequently to rainfall events. Downslope of the forest, soil moisture dynamics were similar to those in other grassland areas and no significant differences were observed beyond 15 m downslope, suggesting minimal impact of the forest at shallow depths downslope. Groundwater levels were lower downslope of the forest compared to other grassland areas, but during the wettest conditions there was evidence of upslope-downslope water table connectivity beneath the forest. The results indicate that forest strips in this environment provide only limited additional sub-surface storage of rainfall inputs in flood events after dry conditions in this temperate catchment setting.

Forest cover has a significant effect on hillslope hydrological processes through its influence on the water balance and flow paths. However, knowledge of how spatial patterns of forest plots control hillslope hydrological dynamics is still poor. The aim of this study was to examine the impact of an across-slope forest strip on sub-surface soil moisture and groundwater dynamics, to give insights into how the structure and orientation of forest cover influences hillslope hydrology. Soil moisture and groundwater dynamics were compared on two transects spanning the same elevation on a 9° hillslope in a temperate UK upland catchment. One transect was located on improved grassland; the other was also on improved grassland but included a 14 m wide strip of 27-year-old mixed forest. Sub-surface moisture dynamics were investigated upslope, underneath and downslope of the forest over 2 years at seasonal and rainfall event timescales. Continuous data from point-based soil moisture sensors and piezometers installed at 0.15, 0.6 and 2.5 m depth were combined with seasonal (~bi-monthly) time-lapse electrical resistivity tomography (ERT) surveys. Significant differences were identified in sub-surface moisture dynamics underneath the forest strip over seasonal timescales: drying of the forest soils was greater, and extended deeper and for longer into the autumn compared to the adjacent grassland soils. Water table levels were also persistently lower in the forest and the forest soils responded less frequently to rainfall events. Downslope of the forest, soil moisture dynamics were similar to those in other grassland areas and no significant differences were observed beyond 15 m downslope, suggesting minimal impact of the forest at shallow depths downslope. Groundwater levels were lower downslope of the forest compared to other grassland areas, but during the wettest conditions there was evidence of upslope-downslope water table connectivity beneath the forest. The results indicate that forest strips in this environment provide only limited additional sub-surface storage of rainfall inputs in flood events after dry conditions in this temperate catchment setting.

The relevance of the study is caused by the necessity to assess the problem of flooding of one of the residential areas in Irkutsk, Irkutsk region. The flooding of urban areas is mostly seasonal. Identifying the conditions of aquicludes and well-permeable rocks, as well as, determining areas of possible groundwater accumulation using the method of electrical resistivity tomography makes it possible to develop measures to eliminate the damage caused by flooding. The objective. The work was carried out using the method of electrical resistivity tomography to assess the geological and hydrogeological conditions for flooding development, which has negative impact on residential development. Objects: bedrock monoliths characterized by high electrical resistance and being practically aquicludes; permeable zones on the land surface, which provide precipitation filtration and ground-water supply through them; areas, where the formation of vadose waters that cause the development of groundwater flooding is possible. Methods: ground geophysical prospecting using the method of electrical resistivity tomography; two- dimensional and three-dimensional inversion of electrical resistivity tomography data and its interpretation with regard to geotechnical drilling data. As a result of ground geophysical prospecting, it was established that the slope on which the assessed territory is located is an ancient landslide cirque, where the natural state of the rock mass is disturbed. Geophysical prospecting has revealed well-permeable zones on the land surface, which provide precipitation filtration and ground-water supply through them. According to electrical resistivity tomography, subzones were identified: severe flooding with groundwater level close to the land surface; moderate flooding with a groundwater level depth of 0,3 to 2 meters and weak flooding with a groundwater level depth of 2,0 to 5,0 meters.

To better understand the subsurface geological composition (relief, fault, fracture, discontinuities, orientation of structures) of the surrounding environment that anticipates infrastructural development in the near future due to population explosion, an Electrical Resistivity Tomography (ERT) survey was conducted in Igarra, Akoko Edo area of Edo state, Nigeria. The depth to bedrock, possible geologic structures (faults, fractures, voids) were some of the properties investigated. To determine the orientation and continuity of the underlying geological features, 2D resistivity surveys were conducted along three parallel traverses (S-N orientation) with a total length of 205m and an inter-traverse spacing of 50m. The ERT results demonstrate that there are constant areas of low resistivity along the three traverses. Stations between 70 m – 90 m and 110 m – 150 m revealed low resistivity values, indicating possible geological structure. As seen in the resistivity pseudo-section, competent beds can be found at around 5 m and about 10 m in some stations (70 – 90 m and 110 – 150 m). It is generally accepted that geological features (fault, fracture) that pose a risk to geotechnical and engineering projects can be found in the regions with low resistivity. According to the research, pervasive underground geological structures are to blame for most road failures. Since electrical resistivity tomography is useful in describing an engineering site, further geophysical investigation for hydrogeological objectives should be undertaken on the identified faulted and fractured zones to establish its hydrologic importance and reserved for such.

This study investigated the Electrical Resistivity Tomography (ERT) A geophysical investigation involving Electrical Resistivity Tomography (ERT) and Vertical Electrical Sounding (VES) for groundwater potentials in Erhoike Community, Delta State, Nigeria, using standard geophysical methods. Six (6) lithologies including the topsoil, dry sand, saturated sand, clayey sand, sandy clay and clay were delineated within the area. The top soil with resistivity and thickness of 547.5 – 8348.6 ohm-m and 0.7 – 1 m respectively represent the first delineated geoelectric layer. This overlies the dry sand having geoelectric parameter of 3.9 – 19.7 m and 761.4 – 8248.6 ohm-m respectively. The dry sand layer underlain by the saturated sand having resistivity ranging from 114.3 – 1380.6 ohm-m. The resistivity of the clayey sand oscillates between 47.6 – 85.3 ohm-m. This layer represents the last layers at the locations where it was delineated, as such the thickness could not be estimated. The clay layer underlies sandy clay in places while in other cases, it succeeds the topsoil. The resistivity and thickness of the clay layer were 11.4 – 48.9 ohm-m and 25.8 – 56.1 m respectively. The sandy clay was found to have resistivity of 50.6 – 115.3 ohm-m and thickness of 2.9 – 8.8 m. The results of the study showed that the saturated sand layer represents the aquiferous layer within the area where groundwater can be tapped for the community. The thickness of this layer is found to be more than 58.2 m which is quite significant for groundwater development. The study concluded that there is abundance of groundwater accumulation beneath the area. It further reinforced the applicability of combined ERT and VES in groundwater potential mapping in an area underlain by similar geology.

Giant aufeis fields are the indicators of water exchange processes in the permafrost zone. The study of aufeis dynamics is relevant to assessing the state of the cryosphere in a changing climate. The Anmangynda aufeis which forms upstream of the Kolyma River basin, was as large as 6.8 km2 in the last century and is considered representative of the mountainous territories in the northeast Russia. In recent decades, there have been significant changes in the aufeis formation regime that require updating the understanding of the cryosphere processes. The historical observational data obtained in 1962-1990 for the Anmangynda aufeis allows using it as the present-day object of research.The main goal of geophysical research in 2021-2022 was to study the structure of the Anmangynda aufeis and aufeis glade to determine its genesis and development processes. The main tasks were to identify the boundary between frozen and unfrozen rocks, to reveal groundwater discharge channels, and to assess the aufeis thickness distribution. There were carried out georadar survey using an antenna unit with central frequency of 250 MHz and ground-based capacitively coupled electrical resistivity tomography. It was found that by April 5, 2021, the maximum ice thickness was 4.35 m with an average value of 1.35 m, and the volume of aufeis was 3.56 million m3. By means of georadar, there were performed identification and drilling verification of the groundwater discharge channels from alluvium to aufeis surface, located in the stream beds. There is geophysical evidence of deep bedrock groundwater sources. Based on the electrical resistivity tomography data, there were identified large and locally freezing river taliks, from which the water is squeezed onto the ice surface. It is recommended to conduct further interdisciplinary research to clarify the geophysical results obtained.

Clays in fault zones have low electrical resistivity, making electrical resistivity tomography (ERT) effective for fault investigations. However, traditional ERT inversion methods struggle to find a unique solution and produce unstable results owing to the ill-posed nature of the problem. To address this, a workflow integrating deep-learning (DL) technology with traditional ERT inversion is proposed. First, a deep-learning model named DL-ERT inversion that maps apparent resistivity data to subsurface resistivity models is developed. To create target-oriented training data, we use approximately 150 field borehole data acquired from various survey areas in South Korea. The DL-ERT inversion algorithm is based on a U-Net structure and includes an additional network called the borehole mixer to incorporate borehole information when available. The DL-ERT inversion model is trained in three stages: base model training, borehole mixer training, and fine-tuning. Results showed that the fine-tuning model provided the highest prediction accuracy for all test datasets. Next, the prediction of the trained model is used as the initial model for the deterministic inversion method to predict the final subsurface model. The efficiency and accuracy of the proposed workflow are demonstrated in fault detection using a field data example compared with traditional deterministic inversion. [ABSTRACT FROM AUTHOR]

The number of large landslides in India has risen in the recent years, due to an increased occurrence of extreme monsoon rainfall events. There is an urgent need to improve our understanding of moisture-induced landslide dynamics, which vary both spatially and temporally. Geophysical methods provide integrated tools to monitor subsurface hydrological processes in unstable slopes at high spatial resolution. They are complementary to more conventional approaches using networks of point sensors, which can provide high temporal resolution information but are severely limited in terms of spatial resolution. Here, we present and discuss data from an electrical resistivity tomography monitoring system—called PRIME—deployed at the Amrita Landslide Early Warning System (Amrita-LEWS) site located in Munnar in the Western Ghats (Kerala, India). The system monitors changes in electrical resistivity in the subsurface of a landslide-prone slope that directly threatens a local community. The monitoring system provides a 4D resistivity model informing on the moisture dynamics in the subsurface of the slope. Results from a 10-month period spanning from pre-monsoon to the end of the monsoon season 2019 are presented and discussed with regard to the spatial variation of soil moisture. The temporal changes in resistivity within the slope are further investigated through the use of time-series clustering and compared to weather and subsurface pore water pressure data. This study sheds new light on the hydrological processes occurring in the shallow subsurface during the monsoon and potentially leading to slope failure. This geophysical approach aims at better understanding and forecasting slope failure to reduce the risk for the local community, thereby providing a powerful tool to be included in local landslide early warning systems. [ABSTRACT FROM AUTHOR]

This article presents the application of electrical resistivity tomography to identify the landslide reactivation hazard. In the absence of borehole data, the correct geological interpretation from field data remains a complex task. This is due to nonlinearity, particularly dissimilarities distributed in the subsurface. Similarly, drilling many boreholes over the landslide susceptible slopes to interpret the final electrical sections is expensive and unsafe. An electrical resistivity survey was performed to evaluate the stability of Huangnibazi earthflow in Sichuan Province, China. In this case, we created three synthetic models representing different subsurface geological characteristics at different depths. A comparison was made between the field and synthetic data to interpret the final electrical resistivity results more accurately. The analysis suggests that the investigated slope has high subsurface saturated conditions, making the existing earthflow debris vulnerable to movement. This study validated the three synthetic scenarios with information from in-suite geological samples. However, applying theoretical models to detect landslide-prone zones in vast areas may effectively locate regions that do not initially appear different from their surroundings but are at high risk of landslides. [ABSTRACT FROM AUTHOR]

In the article, the spring-autumn geoelectrical monitoring of the earthfill dam of a large reservoir is considered. The research was carried out using electrical resistivity tomography (ERT), a contemporary technology for studying the electrical resistivity of a geological medium. Resistivity cross-sections were obtained for different measurement seasons, according to which conducting zones associated with increased filtration of water from the reservoir were detected. The resistivity in anomalous conductive zones changes was established to change depending on the water level in the reservoir, which can reach low values. The research results show the feasibility of seasonal electrometrical monitoring for a more reliable assessment of the state of soil hydrotechnical structures. [ABSTRACT FROM AUTHOR]

Deep soil mixing has been widely used to construct subsurface barriers (cut-off walls) in contaminated sites for contamination containment. Non-invasive geophysical methods are promising for the characterization and assessment of such barriers. The aim of this study was to assess and compare the characterization performance of four geophysical methods (i.e., electrical resistivity tomography, ground-penetrating radar, seismic imaging, and the transient Rayleigh surface wave method) for a subsurface barrier built using soil-mixing technology. The electrical resistivity tomography results show that the overall resistivity of the stratum on the barrier wall increased markedly, and local defects such as pockets of clay appeared as low-resistance anomalies on the resistivity profile. In contrast, the ground radar method failed to make a reasonable evaluation of the quality of the barrier wall because the surrounding environment caused great noise interference. The seismic mapping method had a better performance when the lateral geological conditions were studied. It is also suggested that to improve the signal-to-noise ratio of the surface wave signal, a vibrator with stronger energy should be used, and if conditions permit, the surrounding vibration sources should be shut down during geophysical tests. It is therefore recommended that decision makers and engineers consider using a combination of geophysical methods to evaluate the quality of barrier walls. They should also pay close attention to the specific geological conditions of a survey area, such as the presence of saltwater layers and interference from nearby structures, in order to choose the most appropriate method. [ABSTRACT FROM AUTHOR]

Until recently, evidence of Neanderthal cave use in the Algarve (Southern Portugal) came only from the site of Ibn Ammar. Over the last couple of years, archaeological excavations inside another cave, Gruta da Companheira, yielded Mousterian stone tools associated with possible human fossils. The discovery of this assemblage is groundbreaking because it may contribute to enlighten the Neanderthal/cave relationship and explain the dearth of similar sites in the Algarve. Gruta da Companheira, however, is a complex karst system, which was partly destroyed during its accidental discovery. As result, the original entrance of the cave remains unknown, and it is unclear how sediments, archaeological materials and Neanderthals accessed the site. To tackle these issues, we combined geomorphological observations with speleological, Electrical Resistivity Tomography (ERT) and Ground‐Penetrating Radar (GPR) prospections. Our data indicate that Gruta da Companheira was probably accessed from the hilltop through a sub‐vertical entrance. Additionally, our results suggest the existence of yet unexplored shallower cavities connected with the already known passages of Gruta da Companheira. These results will guide the opening of new excavation areas at the site. The limestone bedrock hosting Gruta da Companheira has been extensively dissolved by karst processes. Therefore, it is necessary to focus future research on the cave infillings to clarify whether Neanderthals exploited the cave's inner chambers or alternatively limited their occupations to the hilltop and geogenic processes reworked their materials into the endokarst system shortly after their stays. The deep karstification and partial collapse of the hill hosting Gruta da Companheira are common in limestone outcrops that occur throughout the Western Algarve. Poor visibility and poor accessibility of this karst area, densely covered with shrubby vegetation, are factors that need to be considered when addressing the scarcity of Middle Palaeolithic cave sites in this region. [ABSTRACT FROM AUTHOR]

In two small and isolated wetlands located at the interface of the Atlantic Forest and Brazilian savanna (Cerrado) in São Paulo State, Brazil, we employed a pixel-based supervised classification approach using a combination of panchromatic and multispectral bands obtained from Landsat 2, 5, 7, and CBERS-04A satellites (ranging from 80 to 2 m/pixel). In addition, we acquired DJI Phantom 4 Pro UAV-RGB images in twelve different periods with a resolution of +5 cm/pixel. Furthermore, we utilized 2D and 3D Electrical Resistivity Tomography (ERT) to obtain data on the surroundings and center of the wetlands. Finally, we conducted a climatological data analysis. The results from the multisource data allowed us to classify the ecosystems as geographically isolated wetlands (GIWs), for which we documented a seasonal month-to-month (12 months) spatial variation of inundated area, vegetation pattern, soil water interaction, and a point of surface and deep-subsurface water interaction. These results are essential for high-accuracy characterization of small wetlands' hydrodynamics and hydroperiods at the local scale. Our study contributes to optimizing GIWs understanding, monitoring, and reapplication of the methodology in other wetlands or small ecosystems. [ABSTRACT FROM AUTHOR]

The cliff in Jastrzębia Góra is one of the most an active landslide areas along the Polish Baltic coast. The aim of these studies was to determine the dynamics of displacements in an active landslide and to identify the geology of the cliff. Two methods, ALS (Airborne Laser Scanning) and ERT (Electrical Resistivity Tomography), were used for this purpose. Multitemporal ALS data were used to determine the geomorphological changes within the cliff and find the causes of the rapid rate of cliff edge landslides. ALS differential models were the sources of new information about the dynamics of vertical displacement in the landslide and helped calculate the volume of displaced rock masses that occurred over 12 years. The cliff was found to become significantly an active in 2010. This process was observed by analysing the relief of multitemporal digital elevation models, differential models, AND morphological sections and by conducting long-term field observations. The ERT surveys made it possible to generate two 3D ERT electrical resistivity models that provided much new information about the geological structure of the cliff. Additionally, a 2D ERT profile was made through the landslide. The internal structure of the landslide was recognized, and the depth of the slip surface was estimated. The results permitted clarifying the cause of the high landslide activity and the rapid rate of retreat of the cliff edge over the past 12 years. In addition, by means of the results of electrical resistivity surveys and the use of archival boreholes, it was possible to extrapolate a model of the surface relief of the clay hill using geostatistical methods. It was found that at the boundary with the active landslide—the top of the clay layer—is tilted towards the north, i.e. towards the sea, which favours the activation of the landslide. The proposed research methodology, as well as the obtained information, may be of significant assistance in further diagnosis and prognosis of the dynamics of landslide development and the causes of landslide formation within cliff coasts. [ABSTRACT FROM AUTHOR]

The productivity of metamorphic aquifers is generally lower than that of the more common alluvial and carbonates ones. However, in some Mediterranean areas, such as the Calabria region (Italy), water scarcity combined with the presence of extensive metamorphic water bodies requires the development of further studies to characterize the hydrodynamic properties of these groundwater systems in order to achieve their sustainable exploitation. The interest in this goal becomes even greater if climate change effects are considered. The purpose of this study was to provide the geological-structural and hydrogeological numerical modeling of a metamorphic aquifer, using direct and indirect data measurement, in a large area of the Sila Piccola in Calabria. The hydrodynamic characterization of the crystalline-metamorphic aquifer, constituted by granite and metamorphic rocks, is extremely complex. The MODFLOW-2005 groundwater model was used to simulate flow phenomena in the aquifer, obtaining hydraulic conductivity values of 2.7 × 10−6 m/s, which turned out to be two orders of magnitude higher than those obtained from the interpretation of the slug-tests performed in the study area. The mathematical model was also able to estimate the presence of a lateral recharge from a neighboring deep aquifer providing a significant water supply to the system under investigation. [ABSTRACT FROM AUTHOR]

Direct current resistivity and electromagnetic methods at low induction numbers are commonly used to characterize near‐surface structures. Although both methods are related to the same property, resistivity or conductivity, they have different sensitivities. The electromagnetic method at low induction numbers is more sensitive to conductive structures, but faces problems resolving resistive bodies, whereas the direct current method can image conductive and resistive variations. Additionally, the electromagnetic method at low induction numbers is less expensive and faster to collect the data, which seems a promising way to provide information at a low cost to enhance the model robustness. Aside from that, the exploration depth in both methods is not the same, but they can complement each other. In this work, a joint inversion algorithm based on a linear approximation was developed to incorporate both data. To achieve the goal, we rewrite the linear integral equations of electromagnetic data at low induction numbers in terms of resistivity logarithm to overcome the differences in magnitude and incorporate both data sets. We explore the potential of the joint inversion testing the algorithm with two synthetic models. In our tests, the joint model improvements are mainly in the conductive geometry and show favourable influence compared to the individual models. Finally, we tested the algorithm with field data collected in the coastal aquifer at Maneadero Valley. Despite the high anthropogenic electromagnetic noise in the area, the joint inversion results are coherent with the individual inversions of electromagnetic soundings at low induction numbers and direct current resistivity along with the geological setting. [ABSTRACT FROM AUTHOR]

Groundwater salinization and pollution are widespread phenomena that degrade water quality and endanger future water exploitation. The problem is intensified in aquifers where human activities result in accelerating water quality deterioration, particularly in arid regions. The elevated salinity can also originate from other natural or anthropogenic processes. In the El Berka region Moulares-Redayef mining basin, water quantity and quality are significant concerns. This study was undertaken to identify, detect, and delineate the sources and extent of salinization of the Pliocene–Quaternary groundwater in El Berka region, using a multi-disciplinary study integrating hydro-geochemical approaches. The aquifer is mainly characterized by high salinity waters (2 to 13 g/L) compared to the surrounding aquifers. The salinity of the groundwater is also impacted by the dissolution of evaporate minerals (anhydrite, gypsum, and halite) in the aquifer. The geophysical approach made it possible to determine the extent of salinity in two particular areas. The first one, located near the mountainous areas and the Tabeditt wadi (valley), is characterized by relatively high resistance, which confirms its low salinity. The second area, in the center of the plain, is dominated by very low resistivity showing the presence of saline water. This study is intended to guide for decision-makers and planners in the water sector in managing groundwater quality. [ABSTRACT FROM AUTHOR]

In the Sangaw region, groundwater is the primary supply of water for drinking, residential purposes, livestock, and summer farming activities. Therefore, the main objective of this research is to delineate groundwater potential zones (GWPZs) in the Sangaw sub-basin, Sulaymaniyah, KRG-Iraq, by integrating geographic information system (GIS), remote sensing (RS), analytical hierarchy process (AHP), and electrical resistivity tomography (ERT) techniques. Seven different thematic layers, including geology, rainfall, slope, lineament density, land use/land cover, drainage density, and topographic position index, were chosen as the prediction factors. The analytical method of an analytical hierarchy process pair-wise matrix was used to evaluate the normalized weight of these thematic layers. All the layers and their corresponding classes were assigned ranks and weights based on their impact on groundwater potential. Using ArcGIS, these thematic maps were combined to precisely determine the groundwater potential map within the research area. Five different potential zones were generated for the resulting map, namely, very low (55.4 km2), low (90.4 km2), moderate (68.1 km2), high (100 km2), and very high (62.4 km2). The findings revealed that almost 43.2% of the study region is characterized by high to very high groundwater potential zones. In contrast, the very low to low groundwater potential covers around 38.7%, and the moderate groundwater potential occupies 18.1% of the study region. The final map was then validated using results from the two-dimensional inverse sections of eight electrical resistivity tomography profiles. The validation data confirmed that groundwater potential classes strongly overlap with the subsurface water-bearing or non-bearing lithology, and groundwater productivity zones in the given area. The novelty of this research lies in the application of electrical resistivity tomography validation to the groundwater potential mapping approach, which illustrates the robustness of the overall methodology for data-scarce areas. Furthermore, this is one of the very few groundwater potential studies in Iraq and the first in the Sangaw sub-basin, which can assist decision-makers with groundwater prospecting and management, and enable further exploration in the region. [ABSTRACT FROM AUTHOR]

Topusko is the second warmest natural thermal water spring area in Croatia, located at the southwest edge of the Pannonian Basin System. Due to favourable geothermal properties, these waters have been used for heating and health and recreational tourism since the 1980s. Thermal springs with temperatures up to 50 °C are the final part of an intermediate-scale hydrothermal system. However, systematic research on the Topusko spring area has not been conducted to lay the foundation for sustainable resource utilisation. Multidisciplinary research including the hydrogeochemical characterisation of naturally emerging thermal water, an electrical resistivity tomography (ERT) investigation conducted to reconstruct the subsurface geology, and hydrogeological parametrisation of the geothermal aquifer was carried out to refine the existing local conceptual model. The results show Ca-HCO3 facies of Topusko thermal waters, which get heated in a Mesozoic carbonate aquifer. The water equilibrium temperature in the geothermal aquifer is estimated to be 78 °C based on the SiO2-quartz geothermometer. The fault damage zone, which enables the upwelling of thermal water, was identified by ERT investigations. The transmissivity values of the aquifer derived from the results of step-drawdown tests range from 1.8 × 10−2 to 2.3 × 10−2 m2/s. Further multidisciplinary research is necessary to improve the existing conceptual model of the Topusko hydrothermal system. [ABSTRACT FROM AUTHOR]

Slope instability occurrences as damaging shallow-landslides in the residual soil around mountains has been widely studied with geophysical, geotechnical and hydrogeological techniques but relating soil electrical resistivity to hydraulic conductivity for characterisation of lithology inducing of these landslides is not common. In this study, we used Electrical Resistivity Tomography (ERT) data and Hydraulic Conductivity (HC) data obtained from soil samples collected within 1–4.5 m depth in the borehole to assess the characteristics of soil that can induce landslide in the study location. The HC data were derived empirically from Beyer, Kozeny-Carman and Slitcher formula which were validated with HC obtained from laboratory experiment. The Empirical Derived Hydraulic Conductivities (EDHC) were correlated with the soil resistivity. The result shows a strong correlation between soil resistivity and HC with regression values of R2 = 0.9702, R2 = 0.9153 and R2 = 0.9232 for Beyer, Kozeny-Carman and Slitcher formula, respectively. The ERT model revealed a possible sliding surface between two contrasting resistive top material and underneath conductive materials at about 4 m depth. The HC assessment result corroborated the ERT model result because high and low-HC values were obtained in the borehole soil samples within 0–4 m and > 4 m depths from EDHC, respectively. The low-HC zone below 4 m depth was responsible for the occurrences of the shallow-landslides in the study. Key points: Relationship between soil electrical resistivity and hydraulic conductivity were examined for assessment of lithology inducing shallow-landslide. Soil electrical resistivity delineated a boundary between two contrasting resistive and conductive lithologies at 4 m depth. Strong correlation ranged between R2 = 0.9153 to 0.9702 were observed between soil resistivity and hydraulic conductivity for the soil samples examined. The conductive lithology with low hydraulic conductivity below 4 m depth was responsible for the occurrences of the shallow-landslides. [ABSTRACT FROM AUTHOR]

Buried bedrock valleys are common erosional features in northern mid-latitude environments that form through glaciofluvial or paleoalluvial processes and are typically infilled by Quaternary-aged sediments. The erosional extent and geometry of the valley including a weathered interface, along with sediment infill that can contain complex sequences of unconsolidated aquifer and aquitard sediments, mean these features may act as preferential pathways to deeper bedrock aquifers. Noninvasive geophysical tools can provide rapid, high-resolution subsurface characterization of these features. This study evaluates the application of electrical resistivity and seismic refraction tomography along two transects centred over a buried bedrock valley in Elora, Ontario, Canada. Geophysical measurements were combined with existing continuous core records and an electrofacies model based on downhole geophysical logs to constrain the morphology and infilled lithostratigraphic architecture of the valley. Bedrock competency associated with lithology may act as a control on depth and width of valley incision during erosion, with resistivity measurements of the bedrock revealing a potential association between interpreted mechanical properties and variations in the resolved valley morphology. Seismic velocity corroborated these contrasting valley widths but could not assess bedrock competency variability below the bedrock interface. This study reveals the sequence of events depositing sediments in the valley, yielding a revised architectural mapping that improves on previous regional scale lithostratigraphic interpretations. Results will be of use to groundwater practitioners requiring detailed conceptualization of this buried bedrock valley and its role on preferential zones of groundwater flow. Similar approaches can be used for delineation of these common and hydrogeologically significant features. [ABSTRACT FROM AUTHOR]

The need to study, protect, and conserve archaeological heritage has enhanced the application of geophysical techniques as non-invasive and reliable tools to investigate fragile and valuable assets. This review presents the most popular geophysical techniques suitable for archaeogeophysical investigations, namely, magnetometry, ground penetrating radar, and electrical resistivity tomography, together with a series of multiparametric measures taken from aerial platforms (UAS). For each method, we recall the basic physical principles, illustrate the operative procedures for field investigation, and provide indications about data processing and modeling. We propose a flowchart to address reliable and effective geophysical investigations, from its planning to the development of the final archaeogeophysical model. We underline the integrated approach, in which the combination of various techniques allows the best results in terms of resolution, coverage, investigation depth, speed, and costs to be obtained. We introduce a suite of studied cases in which this approach has been applied successfully. [ABSTRACT FROM AUTHOR]

The Fens is a region that contributes 11% of the agri-food economy from just 4% of the agricultural land covering England (UK). This region is vulnerable to soil salinisation from sea-level rise with estimated 100-year flood events projected to be observed up to every 2 years by 2100. Seawater intrusion and upwelling of saline groundwater can provide an additional pathway; however, the area's groundwater has not been assessed and the risk is unknown. This study used data from the British Geological Survey's stratigraphic core archive to produce the first stratigraphic map of the loosely consolidated Holocene deposits in the South Holland–Holbeach Marsh region. There is a sandy unconfined aquifer towards the coast, a semiconfined central region with a silty cap and a clay confining cap in the north region. Electrical resistivity tomography data indicate water level depths of 0.58 ± 0.37 m above mean sea level (msl) in February 2021 and 0.01 ± 0.72 m msl in August 2021. The saline–freshwater boundary was at 1.70 ± 0.82 m msl in February 2021, deepening to 2.00 ± 1.02 m msl in August 2021, but the only evidence of seasonal fluctuation was within 10 km of the coast. A potential, but unverified, freshwater lens up to 3.25 m thick may exist beneath the surface. These results suggest that freshwater–saline interface fluctuations may primarily be driven by surface hydrology and would be vulnerable to climate-change-induced future variations in factors that affect surface water. [ABSTRACT FROM AUTHOR]

The establishments of the nexus between the underlying geology and engineering properties are fundamentals to the safe, economic and serviceable designs of civil engineering structures. Cone Penetration Test (CPT) and Electrical Resistivity Tomography (ERT) are critical tools in foundation parameterization especially within Quaternary sediments serving as foundation of engineering structures. Both techniques were used to obtained point data and lateral continuity of geologic units within Ikate Area of Lagos Metropolis for foundation parameterization. Measurements which comprising 4 profiles of 2D resistivity imaging using the Wenner electrode configuration; 1 borehole and 12 cone penetration tests (CPT) were taken with Pasi Terrameter, percussion rig and the 10.0 tons penetrometer respectively. The ERT results interpreted using Dipro software were presented in Pseudo-sections while the cone penetration test results analysed with Microsoft Excel were represented as resistance curves. Interpretation from the two methods integrated with the borehole results reveals the presence clay, peat and sand of varying properties. The uppermost layer consists of medium dense sand followed by clay/peat of very low resistivity (< 3.5 ohm-meter) covering about 6. 0 – 8.0m in depth and terminating in another layer of sand (8.0 – 15.0m). The last sandy layer with cone resistance range between 30 – 120kg/cm2 is considered a suitable layer upon which deep foundation may be founded. Shallow foundation capacity estimates at depths 0.2 – 4.0m derived from direct CPT data using three different computation techniques gives value range from 1.7 – 49.4kg/cm2, 0.7 – 15.2kg/cm2 and 0.4 – 12.6kg/cm2 respectively. Deep foundation for skyscrapers within the area are advised to be founded within the competent layer encountered beyond 10.m depth.

[Display omitted] • Various edge recognition techniques provided detailed structural information. • 2D electrical resistivity tomography and satellite gravity revealed ultrabasic rock. • 2D electrical resistivity tomography revealed faults and contacts between rock unit. • Exploratory drill holes confirmed the underlying presence of thin chromite. The Ingasana Mafic-Ultramafic Complex (IMUC) located in the southwestern Blue Nile region of Sudan, hosts significant chromite deposits of considerable economic importance. Although some preliminary studies have been conducted, however important genetic details, such as integrated geophysical and geological analyses, have not yet been thoroughly investigated. In this study, we conducted a detailed investigation of field features, petrography, and Integrated geophysical surveys in the ore prospect areas of the IMUC for the first time. The aim was to clarify the geological structures and metallogenic characteristics of the region, particularly focusing on the boundaries of rock units associated with chromite deposits. The results from the three-dimensional gravity inversion analysis identify the boundaries between different rock types, including subsurface density variations and major shear zones, revealing that most known mineralization sites are closely associated with structural features and the fault system of the area. Exploratory drill holes (D.H.) of different depths confirm the subsurface occurrence of thin chromite with serpentinite as ven bodies within the ultramafic rocks of Ingasana.On the other hand, Petrological Examinations (P.E.) results identify boundaries between other rocks. These findings further suggest that areas with high-density anomalies are the most favorable for hosting chromium, whereas regions covered with clay rocks exhibit the opposite potential. Furthermore, the study highlights the critical role of fault zones as conduits for magma and mineralizing fluids, emphasizing their significance in controlling the emplacement of mafic–ultramafic rocks and associated mineralization. The integration of geophysical and geological data not only enhances our understanding of the structural framework but also provides a robust basis for future exploration, guiding targeted prospecting efforts for chromite and other related mineral deposits in the IMUC. [ABSTRACT FROM AUTHOR]

• Presentation of the Helguvik pilot project for in-situ CO 2 mineral storage with saline water. • Crosshole seismic and electrical resistivity tomography delineate zones of high and low porosity in the subsurface, highlighting potential pathways for the injected, CO 2 -saturated waters. • Detailed subsurface model of the Helguvik site as a baseline for time-lapse measurements to quantify and locate carbonate precipitation. In-situ CO 2 mineral storage is moving into focus as a technology for storing substantial amounts of CO 2 that would otherwise be released into the atmosphere. However, one of the main drawbacks of this technology is that it requires large amounts of freshwater for injection. To overcome this obstacle, a pilot project in Helguvik, Iceland is testing the effectiveness of carbon mineralization using saline water, similar to seawater. Here, we describe the project and the geophysical characterization of the pilot site using crosshole seismic- and single-hole electrical resistivity measurements. The data show that the subsurface strata are dominated by decameter-thick horizontal layers of basaltic strata, with varying seismic velocities and electrical resistivities. Variations in both seismic velocity and electrical resistivity are in excellent agreement and delineate high and low porosity zones in the subsurface. The results are compared to well logging results and the mineralogical composition of drill cuttings to build a comprehensive subsurface model of the future CO 2 mineral storage reservoir, highlighting potential pathways for the injected CO 2 -charged waters. [ABSTRACT FROM AUTHOR]

On 1 September 2022, a giant loess landslide occurred in Huzhu Tu Autonomous County, Qinghai Province, China. This catastrophic event brought to light a unique loess fluidisation phenomenon. In specific parts of the landslide, the loess completely transformed into a viscous, fluid-like state, whereas other parts showed a deep-seated slide that retained their structural integrity. In this case, loess with different sliding patterns exhibited varying levels of mobility and destructive potential. Based on the field investigation, electrical resistivity tomography was employed to investigate the groundwater condition of the slope. Subsequently, ring-shear tests were carried out to examine the mechanical properties of the sliding zone loess under different saturation degrees and its response to rainfall as a triggering factor. The results indicate that the natural water content in the original slope was unevenly distributed, influenced by local terrain and groundwater runoff. Following the initial slide caused by cumulative rainfall, the overlying sliding material with high degree of saturation was likely to fluidise due to the increase in excess porewater pressure caused by continued shearing, ultimately resulting in flow-like movement features. In contrast, in areas with a deeper groundwater table, the initial shear could only be sustained over a short distance. This study reveals a mechanism of multiple movement patterns that may coexist in giant loess landslides. • A giant loess landslide induced by cumulative rainfall exhibited localised fluidisation phenomenon. • Water content distribution determines the possibility of fluidisation in different parts of sliding body. • Porewater pressure-controlled ring-shear test simulates the process of loess failure and fluidisation. • Minor displacement during deep-seated sliding could lead to the localised fluidsation with an extremely long sliding distance. [ABSTRACT FROM AUTHOR]

Electrical resistivity tomography is a popular geophysical method and has been applied in shallow exploration, involving hydrology, archaeology, and geology, in recent years. To enhance the resolution of electrical resistivity tomography and deal with complex geological settings, we propose the weighted combined inversion of different electrode arrays based on the Jacobian matrix, and then, taking Wenner and dipole-dipole datasets as examples, test its effectiveness on synthetic models and a field case of detecting ancient mausoleum. The results show that the resolution of the weighted combined inversion results is superior to that of a single electrode array in transverse and longitudinal directions, and in the field case, it is demonstrated that the weighted combined inversion algorithm can alleviate the inherent defects of U-shaped electrode array, reduce the ambiguity of inversion, and better constrain the width of the mausoleum.

Comprehensive site investigation techniques, including Electrical Resistivity Tomography (ERT), Induced Polarization (IP), Multichannel Analysis of Surface Waves (MASW), and Microtremor Array Method (MAM), were integrated with geotechnical and geochemical tests of retrieved waste samples from Singapore's operational offshore landfill. The properties of landfill wastes vary widely, including shear-wave velocities 127–248 m/s, densities 1.2–2.1 Mg/m3, resistivity 3.0–25.3 Ω∙m, and chargeability 48–82 mV/V. The natural clay layer underneath was clearly delineated and effectively mitigated leachate leakage. K-means clustering of the geophysical data facilitates precise mapping of waste distribution and quantities of recoverable metals based on quantitative criteria. This study illustrates a thorough case study adopting the new site investigation and characterization paradigm for an offshore landfill, which provides insights into leachate leakage detection and evaluations of landfill mining and resource recovery. [Display omitted] • Geophysical site investigation supplemented with geotechnical and geochemical data. • Delineation of waste-clay boundary and potential leachate leakage detection. • Identification and quantification of waste materials and recoverable metals. • A machine learning-based 3D model for an offshore landfill. [ABSTRACT FROM AUTHOR]

Global warming and human activities are accelerating the degradation of permafrost on the Qinghai-Tibet Plateau (QTP), leading to significant settlement and cracking issues in the local express highway infrastructures. In response, the Gonghe-Yushu Express Highway (GYE) on the east edge of the QTP incorporated extensive cooling measures during its construction to enhance embankment stability. Despite these efforts, field investigations have disclosed that embankment diseases persist across various sections, including those with implemented cooling measures. This study focuses on a specific test and demonstration section of the GYE, employing a suite of cooling measures to assess their engineering effectiveness. Utilizing a combination of multi-time ground-penetrating radar (GPR) and electrical resistivity tomography (ERT) detection, alongside on-site disease investigations and temperature monitoring, this research comprehensively evaluates the efficacy of different cooling interventions. Findings indicate that although cooling measures generally curb permafrost degradation in areas with ice-rich and ice-saturated soils, they fall short in sections with massive ground ice. Of the six cooling measures examined in the demonstration section, ventilation duct embankments emerge as the most effective, whereas crushed-rock layer embankments rank as the least. The study further reveals that the combined use of XPS insulation boards and two-phase closed thermosyphons inadequately addresses the issue of central heat accumulation in broad-width express highways, reducing uneven settlement issues but aggravating longitudinal cracking. Comparative analysis of on-site surveys and monitoring data suggests that regular application of GPR and ERT techniques can proficiently assess the performance of cooling measures. • GPR and ERT effectively evaluate cooling measure performance. • VD embankment most effective，CRL embankment least. • XPS-TPCTs embankment fail to address central heat accumulation. • Composite cooling measures superior to singular measures. [ABSTRACT FROM AUTHOR]

• The combination of non-invasive geophysical methods with minimally invasive techniques improves stratigraphic analysis. • The correlation of EMI data with stratigraphic data enables the development of a validated 3D model of sediment thickness. • The 3D model describes in detail the spatial distribution of buried peat layers and their carbon storage. • A Lower groundwater level may cause peat decomposition and carbon release. This study investigates the stratigraphy and carbon storage of the Verlorener Bach and Loosbach valley fills, of the Alpine Foothills in Bavaria, using a combination of electromagnetic induction (EMI), electrical resistivity tomography (ERT), direct push electrical conductivity sensing (DP-EC) and drilling cores. We identified three distinct stratigraphic units, with Unit I consisting of gravel deposits, Unit II comprising Holocene peat layers, and Unit III containing redeposited carbonates and overbank deposits. The integration of EMI data enhanced spatial resolution, while ERT data provided detailed insights into the thickness and distribution of these units. Correlating EMI-based apparent electrical conductivity values with stratigraphical data enabled the creation of a validated 3D model of sediment thickness. This approach revealed an inverted relief process where non-organic Unit III sediments remain elevated as surrounding organic-rich sediments shrink upon oxidation. Additionally, geochemical analyses estimated the Total Carbon (TC) and Total Organic Carbon (TOC) content for Unit II, totaling 43 kt of TC and 35 kt of TOC across the entire 15-hectare study area. The high carbon storage in peatlands is attributed to the thickness of peat layers and sustained water saturation, preventing degradation. However, potential reductions in groundwater levels could lead to peat decomposition and carbon release. This study demonstrates the effectiveness of integrating EMI, DP-EC and ERT data for stratigraphic analysis, providing a comprehensive understanding of spatial sediment stratigraphies and carbon storage in the study area. Our study demonstrates that it is possible to use geophysical prospecting methods not only to characterise surface sediments but also those located deeper in the ground. This allows for the analysis of both intact fen peats in terms of their carbon storage, as well as those that are no longer intact but buried. [ABSTRACT FROM AUTHOR]

In arid regions like the Eastern Bahira Basin, communities mainly rely on groundwater for drinking and irrigation. However, efficiently managing these vital resources requires a deep understanding of the underlying aquifers' structure and identifying the most suitable areas for exploitation. This presents a significant challenge for the success of water supply and irrigation programs in the Eastern Bahira Basin. This study is based on an integrative approach, combining Electrical Resistivity Tomography data, with the compilation and reinterpretation of pre-existing seismic, gravimetric and vertical electrical sounding data. This approach is based on compiling old gravimetric data and applying advanced processing techniques to determine the horizontal gradient maxima, which helps highlight the major structural alignments in the basin. Furthermore, the approach utilizes seismic data in order to enhance understanding of the deep structure of the basin, reinterpreting it in light of recent drilling data. The interpretation of the gravimetric and seismic data has also been validated by the results of vertical electrical soundings and electrical tomography that we recently acquired in the Eastern Bahira basin. The outcomes of this research provide new insights into the deep structure of the Eastern Bahira Basin and suggest the most promising hydrogeological prospects, thereby contributing to the success of the ongoing drinking water supply and irrigation program in the Eastern Bahira Basin. [ABSTRACT FROM AUTHOR]

Electromagnetic induction (EMI) and electrical resistivity tomography (ERT) are geophysical techniques measuring soil electrical conductivity and providing insights into properties correlated with it to depths of several meters. EMI measures the apparent electrical conductivity (ECa, dS m−1) without physical contact, while ERT acquires apparent electrical resistivity (ERa, ohm m) using electrodes. Both involve mathematical inversion to obtain models of spatial distribution for soil electrical conductivity (σ, mS m−1) and electrical resistivity (ρ, ohm m), respectively, where ρ is the reciprocal of σ. Soil salinity can be assessed from σ over large areas using a calibration process consisting of a regression between σ and the electrical conductivity of the saturated soil paste extract (ECe, dS m−1), used as a proxy for soil salinity. This research aims to compare the prediction abilities of the faster EMI to the more reliable ERT for estimating σ and predicting soil salinity. The study conducted surveys and sampling at four locations with distinct salinity levels in Portugal, analysing the agreement between the techniques, and obtained 2D vertical soil salinity maps. In our case study, the agreement between EMI and ERT models was fairly good in three locations, with σ varying between 50 and 500 mS m−1. However, this was not the case at location 4, where σ exceeded 1000 mS m−1 and EMI significantly underestimated σ when compared to ERT. As for soil salinity prediction, both techniques generally provided satisfactory and comparable regional-level predictions of ECe, and the observed underestimation in EMI models did not significantly affect the overall estimation of soil salinity. Consequently, EMI demonstrated an acceptable level of accuracy in comparison to ERT in our case studies, supporting confidence in utilizing this faster and more practical technique for measuring soil salinity over large areas.

Slope failures are an ongoing global threat leading to significant numbers of fatalities and infrastructure damage. Landslide impact on communities can be reduced using efficient early warning systems to plan mitigation measures and protect elements at risk. This manuscript presents an innovative geophysical approach to monitoring landslide dynamics, which combines electrical resistivity tomography (ERT) and low-frequency distributed acoustic sensing (DAS), and was deployed on a slope representative of many landslides in clay rich lowland slopes. ERT is used to create detailed, dynamic moisture maps that highlight zones of moisture accumulation leading to slope instability. The link between ERT derived soil moisture and the subsequent initiation of slope deformation is confirmed by low-frequency DAS measurements, which were collocated with the ERT measurements and provide changes in strain at unprecedented spatiotemporal resolution. Auxiliary hydrological and slope displacement data support the geophysical interpretation. By revealing critical zones prone to failure, this combined ERT and DAS monitoring approach sheds new light on landslide mechanisms. This study demonstrates the advantage of including subsurface geophysical monitoring techniques to improve landslide early warning approaches, and highlights the importance of relying on observations from different sources to build effective landslide risk management strategies.

Sustainable groundwater management provides an opportunity for environmental water needs to be considered and secured by establishing appropriate groundwater thresholds. Ecosystems that require access to groundwater for some or all their water requirements are referred to as groundwater dependent ecosystems (GDEs). However, large data gaps often exist around the cause-and-effect relationships between groundwater conditions and the impacts they have on GDEs. These data gaps are largely attributed to a lack of shallow monitoring wells near GDEs, and a lack of practical biological metrics to characterize ecosystem health. This transdisciplinary study explores the use of geophysics (electrical resistivity tomography) to fill in our understanding of shallow subsurface soil-hydrological conditions within GDEs. In addition, we develop an approach to characterize ecosystem health within GDEs, using groundwater-dependent vegetation (phreatophytes) as indicators. Ten vegetation variables were used to characterize six biological indicators—growth, diversity, recruitment, structure, native plant dominance, and survivorship—which were used to infer ecosystem health conditions. Health indicators for groundwater-dependent vegetation were found to directly correlate with subsurface conditions, where greater groundwater availability (higher soil moisture content and shallower groundwater levels) was associated with “healthier” vegetation. This study provides a new approach to integrate hydrological, geophysical, and biological data to strengthen monitoring programs and inform water resource management decisions.

The relevance of the study is determined by the need to identify post-mining placers among the original and delineate untouched areas within the reclaimed landfills during prospecting and exploration for placer gold. The task of determining such boundaries in licensed areas arises when subsoil users, starting to develop a field, open up already washed loose deposits left over from predatory mining or unaccounted for production of previous years. The aim: to determine the specific geoelectric features of post-mining and unworked gold placers. Objects: alluvial post-mining placer gold deposits and in natural occurrence. Methods: electrotomography, numerical simulation, field experiment. Results. On the basis of literature data, a geological model of an alluvial placer in natural occurrence was compiled. It includes deposits of spits facies and coastal shallows with nested paleochannel and bedrock. The model of the reclaimed polygon is distinguished by the absence of boulder-pebble deposits of the paleochannel. On the basis of geological models, geoelectric models were compiled. The absence of a high-resistance inclusion in the model of the exhausted polygon is the main difference from the geoelectric model of the original placer. Numerical modeling of electrical tomography data showed that in the electrical resistivity sections, according to the results of 2-D inversion, a sign of a solid placer is the presence of a local high-resistivity anomaly from a paleochannel, and in the case of a reclaimed polygon, a layer in the upper part of the section, consistent in thickness and electrical resistivity. The established signs were revealed during field studies on alluvial placers in Siberia and the Far East. Geoelectric criteria for identifying original and post-mining placers are universal regardless of the study area and geological situation.

In this study, the use of electrical resistivity tomography (ERT) as a tool to guide ornamental stone extraction is investigated. ERT is not conventionally used in highly resistive environments, such as on rock faces, due to the high contact resistances that can impede current injection. Here, the challenges of conducting ERT in such environments are discussed and possible solutions suggested. For this, an example of the application of ERT in a deep and narrow marble quarry is used. The marble deposit is affected by fracturing and karstification. Due to the nature of these features, they present a significant resistivity contrast to the background resistivity of the marble and thus excellent targets to test the application of ERT. Their location was mapped using field observations and complementary ground penetrating radar data. By using an appropriate sensor deployment, a suitable resistivity meter, and advanced data processing routines, the derived 3D resistivity model is in good agreement with the independent observations. This shows that despite the challenges, ERT can be used as a non-invasive tool to obtain information on the stone properties prior to extraction. This will help in guiding quarry operations and will allow for a targeted, safe and efficient extraction of high quality stone, thereby increasing sustainability and economical competitiveness.

Electrical Resistivity Tomography surveys were carried out for the characterization of the Montaguto earth-flow, located in the southern Apennines chain (Campania Region, southern Italy). The earth-flow investigated is one of the largest and most complex landslides in Europe with a length of 3.1 × 103 m, a width ranging between 45 and 420 m and an area of about 6.6 × 105 m2. In the spring of 2010, a large reactivation of the earth-flow heavily damaged some strategic infrastructures. In order to mitigate the effects of the mass movement, considerable efforts were carried out by the Italian National Civil Protection Department (DPC) to tackle the emergency. The aim of the study was to contribute to a more accurate geometric reconstruction of the landslide body and to improve the knowledge of the geological setting. Due to the lithological characteristic of the outcropping lithotypes, i.e. Faeto Flysch (calcarenite, clay and marl) and Villamaina Unit (sand and silty clay), the electrical resistivity contrasts were not very pronounced. However, the high-resolution of the electrical tomographies was the key to observe the presence of both lateral and vertical discontinuities that were associated with lithological boundaries, structural features and sliding surfaces. The results of the geoelectrical surveys could be considered for planning additional and more appropriate actions aimed at the stabilization of different portions of the Montaguto landslide.

Within geoelectrical imaging, the choice of measurement configurations and electrode locations is known to control the image resolution. Previous work has shown that optimized survey designs can provide a model resolution that is superior to standard survey designs. This paper demonstrates a methodology to optimize resolution within a target area, while limiting the number of required electrodes, thereby selecting optimal electrode locations. This is achieved by extending previous work on the 'Compare-R' algorithm, which by calculating updates to the resolution matrix optimizes the model resolution in a target area. Here, an additional weighting factor is introduced that allows to preferentially adding measurement configurations that can be acquired on a given set of electrodes. The performance of the optimization is tested on two synthetic examples and verified with a laboratory study. The effect of the weighting factor is investigated using an acquisition layout comprising a single line of electrodes. The results show that an increasing weight decreases the area of improved resolution, but leads to a smaller number of electrode positions. Imaging results superior to a standard survey design were achieved using 56 per cent fewer electrodes. The performance was also tested on a 3-D acquisition grid, where superior resolution within a target at the base of an embankment was achieved using 22 per cent fewer electrodes than a comparable standard survey. The effect of the underlying resistivity distribution on the performance of the optimization was investigated and it was shown that even strong resistivity contrasts only have minor impact. The synthetic results were verified in a laboratory tank experiment, where notable image improvements were achieved. This work shows that optimized surveys can be designed that have a resolution superior to standard survey designs, while requiring significantly fewer electrodes. This methodology thereby provides a means for improving the efficiency of geoelectrical imaging.

• A machine learning-based approach is proposed for leachate detection. • We apply our multivariate analysis to two study cases of urban landfills. • Geoelectrical tomography data are clustered to get integrated models. • Different levels of leachate contaminations are identified by cluster analysis. • Our multivariate analysis helps predicting the possible leachate flow pathways. Leachate is the main source of pollution in landfills and its negative impacts continue for several years even after landfill closure. In recent years, geophysical methods are recognized as effective tools for providing an imaging of the leachate plume. However, they produce subsurface cross-sections in terms of individual physical quantities, leaving room for ambiguities on interpretation of geophysical models and uncertainties in the definition of contaminated zones. In this work, we propose a machine learning-based approach for mapping leachate contamination through an effective integration of geoelectrical tomographic data. We apply the proposed approach for the characterization of two urban landfills. For both cases, we perform a multivariate analysis on datasets consisting of electrical resistivity, chargeability and normalized chargeability (chargeability-to-resistivity ratio) data extracted from previously inverted model sections. By executing a K-Means cluster analysis, we find that the best partition of the two datasets contains ten and eleven classes, respectively. From such classes and also introducing a distance-based colour code, we get updated cross-sections and provide an easy and less ambiguous identification of the leachate accumulation zones. The latter turn out to be characterized by coordinate values of cluster centroids<3 Ωm and >27 mV/V and 11 mS/m. Our findings, also supported by borehole data for one of the investigation sites, show that the combined use of geophysical imaging and unsupervised machine learning is promising and can yield new perspectives for the characterization of leachate distribution and pollution assessment in landfills. [ABSTRACT FROM AUTHOR]

• LDI-MVFNet fuses three electrode arrays to improve precision of leachate imaging. • Field salt tracer experiments simulate media changes caused by pollutant diffusion. • The proposed algorithm compensates the deficiencies of single-ERT imaging. • Distribution of contaminant plumes was more accurately delimited. • The method provides guidance for site risk assessment and efficient remediation. The accurate monitoring and early warning of groundwater pollution caused by the concealed leakage of landfills is a major challenge globally in the field of solid waste management and groundwater protection. Electrical resistivity tomography (ERT) represents a potential solution with advantages, owing to its fast and nondestructive characteristics. However, traditional ERT based on a single array cannot reveal the distribution and dynamics of pollution in complex underground media owing to the limited information it carries. We designed a novel deep network for multi-view fusion to invert the real resistivity distribution of the medium caused by leachate (named LDI-MVFNet) so as to infer the distribution of leachate. To support model establishment and validation, ERT instances collected from synthetic models and a salt tracer experiment were inverted. We compared the inversion results of the LDI-MVFNet with those of single arrays and found that the LDI-MVFNet performed the best overall. The average root mean square error (RMSE) of synthetic models reached 0.98, performing better than Dipole–Dipole (3.86), Wenner–Schlumberger (3.37), and Pole–Pole (6.61), which were inverted separately. The resultant inverted subsurface true resistivity data were presented in the form of two-dimensional (2D) cross sections. The imaging results of 2D cross sections showed that LDI-MVFNet was superior to others in data noise suppression and inversion accuracy. The results of this study indicate that the data fusion of multiple views can more accurately reflect the real resistivity than the inversion of a single array can. [ABSTRACT FROM AUTHOR]

Geophysical and geochemical methods were applied to detect the subsurface setting of an Upper Pleistocene-Holocene fluvial incised-valley where a travertine body intercalates between alluvial deposits of the Tiber river (central Italy), at Prima Porta (close to Rome). This study allowed us to provide more information regarding the local stratigraphic architecture and structural features, as a reference analogue to similar settings: i.e., hard (stiff) lithic travertines buried below fine and loose alluvial plain covers. Two Electrical Resistivity Tomography (ERT) profiles, interpreted and calibrated using previously collected litho-stratigraphic data from a borehole, identified a massive body, with a relatively high resistivity that correlates with the travertine deposit of Prima Porta. In addition to ERT, ambient noise measurements, processed with the HVSR technique and 2D array, and seismic refraction tomography were carried out; HVSR data were highly consistent with ERT results and allowed to discriminate between the travertine body and the silty-sand channels and overbank deposits, which were attributed to the Tiber river's evolution during Upper Pleistocene-Holocene. Finally, the presence of cracks/fractures could be inferred, as suggested by slight polarisation effects recorded in the HVSR results and soil-gas anomalies. [ABSTRACT FROM AUTHOR]

Human engineering activities and climate warming induce permafrost degradation in the Da Xing'anling Mountains, which may affect the distribution of permafrost and the safety of infrastructure. This study uses the electrical resistivity tomography method, in combination with field surveys and ground temperature monitoring, to investigate the distribution and degradation characteristics of permafrost and influencing factors at a typical monitoring site (MDS304) near the China-Russia Crude Oil Pipeline (CRCOP). The results show that the isolated permafrost in this area is vulnerable to further degradation because of warm oil pipelines and thermal erosion of rivers and ponds. The isolated permafrost is degrading in three directions at the MDS304 site. Specifically, the boundary between permafrost and talik is on both sides of the CRCOP, and permafrost is distributed as islands along a cross-section with a length of about 58–60 m. At present, the vertical hydrothermal influence range of the CRCOP increased to about 10–12 m. The active layer thickness has increased at a rate of 2.0 m/a from about 2.4–6.8 m to 2.5–10.8 m from 2019 to 2021 along this cross-section. Permafrost degradation on the side of the CRCOP's second line is more visible due to the river's lateral thermal erosion, where the talik boundary has moved eastward about 12 m during 2018–2022 at a rate of 3.0 m/a. It is 2.25 times the westward moving speed of the talik boundary on one side of the CRCOP's first line. In contrast, the talik boundary between the CRCOP's first line and the G111 highway also moves westward by about 4 m in 2019–2022. Moreover, the maximum displacement of the CRCOP's second line caused by the thawing of frozen soil has reached up to 1.78 m. The degradation of permafrost may threaten the long-term stability of the pipeline. Moreover, the research results can provide a useful reference for decision-makers to reduce the risk of pipeline freeze-thaw hazards. [ABSTRACT FROM AUTHOR]

Recharge between a river and shallow aquifer in a floodplain involves critical hydrological processes for the whole ecological environment, which often exhibits heterogeneity because of seasonality and geological complexity. In this study, electrical resistivity tomography (ERT) was used to analyze the temporal and spatial variations in the recharge characteristics of a floodplain under a variety of climatic and geological conditions. Two sets of ERT tests (in the dry season and wet season) were conducted. Each test included four ERT lines to capture the dynamic electrical resistivity distribution associated with season-driven, river and shallow groundwater interactions along a stretch of the Yellow River (adjacent to the floodplain) in China. The findings indicate that this floodplain is composed of three distinct hydrogeological units. Additionally, ERT images taken during the wet season demonstrate that river water recharges the shallow aquifer and then flows toward the middle aquifer via several seepage channels. Based on time-lapse ERT images, different recharge characteristics are identified in the low and high floodplain. In the low floodplain, both the Yellow River and the vadose zone are preferential shallow groundwater recharge zones. In the high floodplain plain, only the vadose zone is a preferential shallow groundwater recharge zone. Resistivity mapping can provide valuable information about the recharge between surface-water bodies and shallow aquifers. This is particularly useful when combined with water level data, and resistivity distribution with depth can also be used to characterize the stratigraphic structure of the floodplain. [ABSTRACT FROM AUTHOR]

Long-term draining of peatlands results in transformation of vegetation and obliteration of their morphological features. In many areas, efforts are made to restore the original ecosystems and increase their water retention potential. Using combined analyses of a LiDAR-based digital terrain model (DTM), colour-infrared (CIR) imagery data, ground-penetrating radar (GPR) data and electrical resistivity tomography (ERT) data, we tested the applicability of these methods in outlining the extent and subsurface structure of drained mires located in the Stolowe Mountains National Park area, Poland. The LiDAR-DTMs enabled parameterisation of physiographic features of the mires and determination of their extent, runoff directions and potential waterlogging areas. CIR analysis enabled classification of vegetation types. GPR prospecting revealed the bedrock morphology, thickness and internal structure of the peat deposits, showing that this technique can also provide data on variability in the decomposition of phytogenic deposits. The obtained ERT sections indicate both the thickness of peat deposits and variability in the bedrock internal structure. The results show that integrated analyses of data obtained with different methods can be an effective tool in outlining the original extent of peatlands, with potential application in the planning of peatland ecosystem restitution. [ABSTRACT FROM AUTHOR]

Deciphering the internal composition of large-scale fault zone is a prerequisite for constructing conceptual models of fault zone architecture and is essential for a proper understanding of the seismological, mechanical and hydrological properties of fault zones. To this end, we conducted fine detection and interpretation of a large-scale fault (F31 fault) in the first Chinese underground research laboratory (URL) construction site for high-level radioactive waste geological disposal repository to elucidate the fault zone architecture. The fault, located in the west of the URL site, is an approximately 5.5-km scale steeply dipping normal fault extending continuously in a straight line. In this study, geophysical prospecting techniques including high-density electrical resistivity tomography (ERT) and reflection seismic tomography (RST) were employed to investigate and interpret the subsurface architecture of the fault zone along the strike of fault core and perpendicular to fault core, respectively. In addition, a 4-m long three-dimensional prospecting trench was excavated manually to observe the geological structure characteristics of the fault zone. Geophysical exploration results suggested that the shallow surface within the fault zone, which is mainly characterized by low conductivity and low wave velocity transmission medium, shows complex geological characteristics due to severe weathering, while the relatively complete bedrock lies beneath the overburden layer. Along the fault strike, the bedrock is buried shallowly at the south of the fault zone. In contrast, at the north, it is mainly characterized by a thick weathering layer overlying the bedrock. For the detection results of vertical fault core, both geophysical methods have deciphered the location of the fault core and the spatial distribution characteristics of F31 fault zone. However, compared with RST results, ERT also clearly diagnosed that there is another secondary fault zone with a certain scale at the hanging wall of F31 fault. In terms of the F31 fault core, ERT suggested that the fault dips about 70° NW and the width of the fault core is 2 – 5 m, which is consistent with the results of the 280° ∠ 75° discontinuities and the approximately 2.6-m long fault core revealed by the prospecting trench. These results provide an important basis for further understanding the internal structure of faults in this site and the avoidance design of the fault-affected range for the underground engineering layout. [ABSTRACT FROM AUTHOR]

A set of geological and geophysical works has been carried out to study fracturing in the Jurassic–Neogene rocks of the Heracles Plateau, which included a field study of the Georgievsky fault zone and a structural and geomorphological analysis; the geophysical complex included marine seismic and magnetometric studies combined with ground-based studies using electrical resistivity tomography, gravimetry, and magnetometry. The main objects of study were the zone of the deep Georgievsky fault and feathering tectonic disturbances. Our integrated research revealed the main geological and geophysical criteria for identifying dangerous fracturing sites: an extremely heterogeneous structure of the upper part of the geoelectric section to depths of 30–40 m according to electrical survey data; seismic data indicate that Miocene limestones have extremely low strength properties in areas with increased fracturing; according to electrical survey data, the water content (humidity) of the upper part of the section changes sharply horizontally; in the karst areas, the resistivity varies sharply from the maximum values to minimum ones at certain depths. Tensile fractures that occur in areas of the positive relief of base rocks, along which landslide bodies represented by limestones flow, are particularly dangerous. [ABSTRACT FROM AUTHOR]

Both hydrological and geophysical data can be used to calibrate hillslope hydrologic models. However, these data often reflect hydrological dynamics occurring at disparate spatial scales. Their use as sole objectives in model calibrations may thus result in different optimum hydraulic parameters and hydrologic model behavior. This is especially true for mountain hillslopes where the subsurface is often heterogeneous and the representative elementary volume can be on the scale of several m3. This study explores differences in hydraulic parameters and hillslope‐scale storage and flux dynamics of models calibrated with different hydrological and geophysical data. Soil water content, groundwater level, and two time‐lapse electrical resistivity tomography (ERT) data sets (transfer resistance and inverted resistivity) from two mountain hillslopes in Wyoming, USA, are used to calibrate physics‐based surface–subsurface hydrologic models of the hillslopes. Calibrations are performed using each data set independently and all data together resulting in five calibrated parameter sets at each site. Model predicted hillslope runoff and internal hydrological dynamics vary significantly depending on the calibration data set. Results indicate that water content calibration data yield models that overestimate near‐surface water storage in mountain hillslopes. Groundwater level calibration data yield models that more reasonably represent hillslope‐scale storage and flux dynamics. Additionally, ERT calibration data yield models with reasonable hillslope runoff predictions but relatively poor predictions of internal hillslope dynamics. These observations highlight the importance of carefully selecting data for hydrologic model calibration in mountain environments. Poor selection of calibration data may yield models with limited predictive capability depending on modeling goals and model complexity. Key Points: Water content calibration data yield models that overestimate near‐surface water storage in mountain hillslopesGroundwater level calibration data yield models that reasonably represent hillslope‐scale storage and flux dynamicsResistivity calibration data yield models with reasonable hillslope runoff predictions but poor predictions of internal hillslope dynamics [ABSTRACT FROM AUTHOR]