Geophysical Surveys Research Articles

Developing a conceptual model of groundwater – Surface water interactions in a drought sensitive lowland catchment using multi-proxy data

Frequencies and intensities of droughts have increased due to climate change, providing an urgent impetus to improve understanding of ecohydrological fluxes in drought-sensitive areas where water and food security are threatened. We used a multi-proxy approach for assessing the effects of landuse and catchment properties on recharge and groundwater – surface water interactions during a prolonged drought starting in summer 2018 in a 66 km2 lowland, mixed landuse catchment (Demnitzer Mill Creek, Germany). We used water table monitoring, water stable isotopes, tritium isotopes, hydrogeochemical tracers, streamflow observations and geophysical investigations to characterise the spatial and temporal patterns of groundwater recharge in a shallow, unconfined aquifer system. Long-term groundwater levels showed a declining trend since 2011, which accelerated after 2018 resulting in increasingly intermittent streamflow. Geophysical surveys and groundwater monitoring indicated that shallow water tables (typically < 3 m deep) in low to moderate permeability surficial deposits are generally recharged during winter, leading to higher groundwater – surface water connectivity in riparian alluvial aquifers, which is the first order control on streamflow generation. This was supported by similar geochemical characteristics of groundwater and streamflow. Water stable isotopes indicated a high damping in groundwater with a bias towards winter precipitation and direct recharge. Groundwater age estimates using tritium showed high uncertainty but indicated that shallow groundwater was < 10 years old and generally similar to streamflow. Such multi-proxy approaches help understand changes in groundwater recharge and stream-aquifer interactions during droughts and contribute to the development of sustainable land and water management strategies for groundwater systems that are sensitive to climate change.

Factors influencing the creation of high-impact oil and gas geophysical seismic cutlines in an ecologically-sensitive landscape in northeastern British Columbia, Canada

Oil and gas (OG) resource extraction has adverse impacts on landscapes despite the socio-economic benefits that trickle down to society. Whereas many recent studies have focused on direct landscape change from OG activities, this study focuses on factors associated with the creation of high-impact OG seismic cutlines, geophysical survey paths that have widths of more than 5.5 m. Using geographic information systems and a spatially-explicit logistic regression framework, we model the relationship between high-impact seismic cutlines and associated explanatory variables (e.g., seismic cutline type, land ownership type, etc.) by drawing on political ecology perspectives. The study finds that mechanically-cut seismic cutlines are 514.34 times significantly more likely to be high-impact seismic cutlines as compared to hand-cut seismic cutlines. We find that seismic cutlines found on private land are 0.05 times significantly less likely to be high-impact type as compared to those found on crown (public) land. These findings suggest that societal land use decisions and preferences are likely to influence the creation of spaces for different levels of OG land user–environment interactions. Thus, land use managers are presented with unique land use challenges that require environmental management strategies for dealing with the impacts of OG activities on the environment.

Application of Electrical Resistivity Method to Decipher Groundwater Occurrence Status at Isikuku, Southern Nigeria

Electrical resistivity method is a type of geophysical survey employed for groundwater investigation, conducted in Isikuku Community in Benin City, Edo state with the aim of delineating groundwater occurrence. Schlumberger electrode array configuration was employed in this study. Six (6) VES points were surveyed with linearised inversion technique used for the interpretation of sounding taken at various locations in the area. The data collected were interpreted by curved matching and computer iteration using Interpex Ix1D v 2 software. From the geoelectric section, VES 1 possess the AK curve with four layers ρ1˂ρ2˂ρ3˃ρ4, VES 2 possess the KQ curve with four layers ρ1˂ρ2˃ρ3˃ρ4, VES 3 possess the A curve with three layers ρ1˂ρ2˂ρ3, VES 4 possess the AK curve with four layers ρ1˂ρ2˂ρ3˃ρ4, VES 5 possess the A curve with three layers ρ1˂ρ2˂ρ3, VES 6 possess the K curve with three layers ρ1˂ρ2˃ρ3. Geo-electrical layers identified in the study area included topsoil, sandy clay, clay basement and sandstone. The VES study revealed the layer which constitute the productive water-bearing zones referred to as good groundwater potential aquifers. The analysis of the interpretation of the field data showed that the area under investigation delineated four layers earth in each of the vertical electrical sounding point. Generally, the geoelectric survey conducted in the study area revealed the subsurface lithologies: Clay, Clayey Sandstone, Sand stone, Coarse Sand, Lateritic soil and Top soil. Thus, vertical electrical sounding techniques employed in this study has proved useful and successful in delineating subsurface lithology in the study area.

A Numerical Output Technique for Voxler’s ObliqueImages and Its Application

In geophysical surveys, there will be no measured data at some location where it is inaccessible for placement of survey points or lines. The interpolation data of those locations can be obtained and displayed by using three-dimensional (3D) mapping platform. Based on the study of the file format of ObliqueImage output in Voxler platform, this paper presents a technique for extracting spatial coordinates and physical parameter values of each point in the ObliqueImage. This numerical output technique is used to map the profiled slice across the tunnel axis where boreholes can not be arranged in the electromagnetic wave CT investigation section in a dedicated karst survey of an underwater tunnel in Wuhan, rendering the karst development on the profile across the tunnel axis; after further extension, the point cloud data of bedrock surface and karst caves for building 3D geological model are extracted from isosurface files, which provides data basis for tunnel design and construction digitization.

Marine Geophysical Survey of a Medieval Shipwreck in Shallow Waters Using an Autonomous Surface Vehicle: A Case Study from Avaldsnes, Norway

This study demonstrates the successful use of a single-channel chirp system mounted on an Autonomous Surface Vehicle (ASV) for detecting and mapping a partly buried medieval ship found in water approximately one meter (m) deep in a dynamic, intertidal environment at Avaldsnes, south-western Norway. The ASV's fast mobilization and access to areas otherwise difficult to reach, makes it an efficient, low-cost, and non-invasive platform for examining the seafloor and subsurface with high-resolution seismic data, acquired in a dense grid. Line spacing of 0.25 m allowed for the generation of a detailed 3D data cube, enabling effective interpretation of both acoustic vertical sections and horizontal amplitude maps. This approach empowered accurate identification of the outline of the wooden hull and provided information about ship dimensions and maximum burial depth. Structural elements observed in the geophysical datasets, including the keelson, raiders, and maststep, corroborates with findings from previous diving investigations and photogrammetry documentation. Moreover, the geophysical survey offers valuable additional knowledge of the buried ship remains, revealing a slight tilt of the keel and a substantial object buried in close proximity to the stern, probably the rudder or another wreck-related artefact.

Engineering geological conditions for the construction of a photovoltaic power plant on coal tailings

Photovoltaic power plants have recently become increasingly common to reduce carbon emissions into the atmosphere. Non-fertile lands occupied by industrial waste are very suitable for their construction. The present study concerns the design and construction of a photovoltaic park on the territory of a reclaimed coal tailings dump “Suhoto Dere” near the TPP “Bobov Dol”. The study includes collection, processing and analysis of archival materials, site mapping, drilling of exploration boreholes, dynamic penetration tests, geophysical electrical resistivity survey, laboratory testing of soil samples to determine physical and mechanical properties; chemical analysis of soil samples to assess soil aggressiveness to concrete and steel. Based on the obtained data, an assessment of the suitability of the site is made and recommendations are given to prevent the occurrence of adverse phenomena and processes.

Heat Flow Prediction in Songliao Basin Based on Deep Neural Network

The heat flow is the key data for accurately predicting the contribution of underground heat, but due to the high cost of measurement, the spatial difference is huge, and the heat flow information in some areas is little known. This paper uses deep neural network technology to perform machine learning on a large number of relevant geological and geophysical features and heat flow measurements on a global scale. In addition, the model uncertainty quantification process is introduced, and the reliability of the prediction results is discussed based on the global sensitivity analysis and correlation calculation of the deep learning method. Finally, for the distribution map of heat flow and absolute difference in the Songliao Basin in the study area, the measured data error is less than 11%, and the predicted absolute difference is less than ±20 mW/m2. The results prove the accuracy of the method and the abnormal high heat flow in the central region of the basin. The existence of, further combined with the results of geophysical surveys, provides evidence for the analysis of regional thermal causes.

Defining of prospective areas for the localization of groundwater in fractured massifs (on the example of the Municipality of Brezovo, Plovdiv Region)

The northern part of the Municipality of Brezovo falls within the range of a fractured massif, which predetermines the presence of springs with a limited flow rate, insufficient for water supply for the villages there, which necessitates the localization of suitable locations for boreholes drilling. After a complex assessment of the geological-hydrogeological and tectonic conditions and field surveys, favorable sections were determined with prerequisites for the presence of probable water-saturated fractured zones. As a result of geophysical surveys carried out using the SP method, in the area of the villages of Svezhen, Chehlare and Rozovets, deep water-bearing zones were delineated, which were convincingly confirmed during the subsequent exploratory drilling.

THE ZABAIKALIAN PARAMETRIC BOREHOLE: A FIRST EVIDENCE ABOUT DEEP STRUCTURE OF THE BORSHCHOVOCHNY METAMORPHIC CORE COMPLEX

The Zabaikalian parametric borehole drilled out a metamorphic core complex on the reference geological and geophysical profile within the Central Asian fold belt, south of the Mongol-Okhotsk suture zone. In the section of the borehole drilled to a depth of 2600 m, a set of geophysical, geological and laboratory-analytical studies identified three main structural elements of metamorphic core complexes: the upper plate, detachment, and the lower plate. The upper plate (weakly metamorphosed rocks) is represented by serpentinite melange, which is separated from the underlying rocks of the lower plate by a zone of chlorite breccias (detachment). The lower plate, which is part of the crystalline basement complex, includes rocks of granite-schist and granite-plagiogneiss subcomplexes. The granite-schist subcomplex is composed of mafic and intermediate schist with amphibolites and quartzites. Biotite granite is widespread in the section; it forms layered veins with signs of synkinematic formations. According to preliminary estimates, the age of biotite granite is about 130 Ma. The schist is characterized by mylonite structure at intervals of interbedding with biotite granite veins. In accordance with data of geophysical surveys in the borehole and the petrophysical characteristics of cored rocks, the mylonite zone is the provenance of a series of inclined reflectors on the seismic reflection-CDP section, which can be traced to a depth of at least 10 km. The granite-plagiogneiss subcomplex is represented by plagiogneiss, leucogranites, and gneissic granites. In the Zabaikalian parametric borehole, a detailed section of the orshchovochny metamorphic core complex, fully characterized by core samples, of the was obtained, which should be considered as a reference for studying these structures. The investigation of this section will answer later many questions about the formation and evolution of the Central Asian fold belt.

Discovery of an Active Forearc Fault in an Urban Region: Holocene Rupture on the XEOLXELEK‐Elk Lake Fault, Victoria, British Columbia, Canada

AbstractSubduction forearcs are subject to seismic hazard from upper plate faults that are often invisible to instrumental monitoring networks. Identifying active faults in forearcs therefore requires integration of geomorphic, geologic, and paleoseismic data. We demonstrate the utility of a combined approach in a densely populated region of Vancouver Island, Canada, by combining remote sensing, historical imagery, field investigations, and shallow geophysical surveys to identify a previously unrecognized active fault, the XEOLXELEK‐Elk Lake fault, in the northern Cascadia forearc, ∼10 km north of the city of Victoria. Lidar‐derived digital terrain models and historical air photos show a ∼2.5‐m‐high scarp along the surface of a Quaternary drumlinoid ridge. Paleoseismic trenching and electrical resistivity tomography surveys across the scarp reveal a single reverse‐slip earthquake produced a fault‐propagation fold above a blind southwest‐dipping fault. Five geologically plausible chronological models of radiocarbon dated charcoal constrain the likely earthquake age to between 4.7 and 2.3 ka. Fault‐propagation fold modeling indicates ∼3.2 m of reverse slip on a blind, 50° southwest‐dipping fault can reproduce the observed deformation. Fault scaling relations suggest a M 6.1–7.6 earthquake with a 13 to 73‐km‐long surface rupture and 2.3–3.2 m of dip slip may be responsible for the deformation observed in the paleoseismic trench. An earthquake near this magnitude in Greater Victoria could result in major damage, and our results highlight the importance of augmenting instrumental monitoring networks with remote sensing and field studies to identify and characterize active faults in similarily challenging environments.

On the application of Transient Electromagnetics (TEM) and DC-resistivity methods for groundwater level detection in the Cipatat karst area

Due to mountainous morphology, meeting the freshwater demand for daily consumption in some villages in the Citatah karst area is problematic. Some water springs exist in some parts of the valley and slopes. The water flows through pipes connecting people’s houses by pumping it using electricity. To know the potential of the groundwater in the area, we conducted geophysical surveys in a test area close to known dig wells. These are Transient Electromagnetic (TEM) and DC-resistivity methods. TEM data were collected using an in–loop transmitter-receiver configuration with Temfast 48 devices with 5 m × 5 m and 10 m × 10 m wire loops. We acquired resistivity data using a 4-point light 10w IP device, producing resistivity and chargeability data. In this preliminary result, we show only resistivity distribution. We validated the processed TEM and resistivity data with the data from seven dig wells. Our results deliver good results. The resistivity data reveals low resistivity anomalies ranging from 26.5 Ωm to 58.5 Ωm. This low resistivity zone lies at 0.6 m – 1.45 m depth associated with groundwater level.

UAV-based aeromagnetic surveys for orphaned well location: Emerging best practices

Historical oil and gas exploration and development in the northeastern United States left behind hundreds of thousands of orphaned oil and gas wells in areas where hydrocarbon extraction predated state and federal regulations on well abandonment. Abandoned by their original operators with incomplete records of location and well status, orphaned wells pose significant economic and environmental challenges associated with possible emissions of formation liquids and gases. Effective location and assessment of orphaned wells is a key first step in well site remediation; however, the task of locating orphaned wells has proven to be a formidable challenge in some of the most impacted areas. Specifically, in key areas of the northeastern United States, where the oil and gas industry first emerged in the late 19th and early 20th centuries, historical lease maps have proven largely inaccurate, and wide-area terrestrial geophysical surveys in difficult terrain characteristics and dense vegetation were found to be cost-prohibitive. In recent years, integration of miniaturized magnetic sensors with low-altitude uncrewed aerial vehicles (UAVs) facilitated successful implementation of wide-area aeromagnetic surveys targeting orphaned well identification in areas where piloted aeromagnetic surveys were previously infeasible due to challenging terrain and canopy conditions. Aeromagnetic data sets collected by ultra-low-altitude UAV surveys and processed to highlight magnetic anomalies associated with orphaned well casings have the potential to drastically reduce search areas for orphaned wells and complement ground surveys, thus helping turn the tide in orphaned well remediation efforts. As UAV-based aeromagnetic surveys gain recognition as a dependable wide-area surveying tool for remote identification of orphaned well sites, we highlight key advantages and important limitations of this methodology, underscore key practical challenges to successful implementation, and outline best practices in effective survey design and execution.

Информационный потенциал разрушенных погребений саргатской культуры: курган Новопокровка 16 в Среднем Прииртышье

The article deals with a complex study of the materials obtained during archaeological excavation of the kurgan Novopokrovka 16 in the middle Irtysh river basin (Omsk region). The site, which is attributed to the Sargat culture (5th century BC – second half of the 3rd century AD), was located farmost on the right bank of the river Irtysh, nearby the group of “Princely kurgans”. Despite almost total disturbance by robbers and agricultural activity, common scholars’ efforts demonstrate high informative capacity of the multidisciplinary approach, while modern level of undertaken research is not just being declared but enables to reconstruct seemingly lost information. The kurgan erection stages and mound structure features have been decoded using the results of a geophysical survey and soil morphology data. The paleoanthropological study of the incomplete skeletal remains does not support multiple or inlet interment inside the central grave, and provides sexing and aging of the buried individuals as well as some paleopathological observations. Apart from species examination, archaeozoological data testify that a warm period from spring to early autumn was the season of animal slaughter. Characteristics of mortuary rituals and direction of intercultural contacts of the ancient forest-steppe groups have been completed by new details based on the results of strontium isotope analyses (dental enamel of humans and animals) and evidence non-local origin of the individual buried under the excavated kurgan, what is different from local origin of horses butchered for funereal feasts. The proposed hypothesis supports previously suggested archaeological, paleoanthropological and paleogenetic facts on the origin of the forest-steppe population, indicating an involvement of various population groups with notable external components. Based on the archaeological materials, the kurgan under study might be dated back to mid-4th – 3rd centuries BC.

Application of OCTEM in The Detection of Hidden Faults in Urban Underground Space Investigation

At present, the geological survey of urban underground space is currently being carried out in many cities across the country. Choosing appropriate survey methods will make this work more effective. OCTEM is a new exploration method that has emerged in engineering geophysical prospecting in recent years. It has the advantages of portable facilities and strong anti-interference ability, and is suitable for urban geological survey work. In this paper, OCTEM is applied to the hidden fault detection work in underground space survey in Chengdu. The results show that this method can effectively identify the fault fracture zone in the strong interference urban environment. At the same time, the OCTEM results are compared with the application results of the other 2 geophysical methods. The analysis further proves the adaptability and superiority of this method. It provides an effective new method for urban underground space survey work.

Application of Borehole Geophysical Prospecting Method in Pile Foundation Detection of Existing Buildings

It is particularly important to find out the pile foundation of existing buildings for building safety protection and engineering construction safety during the development and utilization of urban underground space. As a non-destructive, efficient and economic method, the borehole geophysical techniques such as magnetic gradient method, ground penetrating radar method and parallel seismic test method are used to detect the pile foundation of existing buildings, which have obvious advantages. According to the combined abnormal characteristics such as "strong magnetic anomaly, electromagnetic wave in-phase axis change and diffraction wave anomaly at the pile end, P-wave velocity variation", the pile foundation length can be judged.

An attempt to use convolutional neural network to recover layered-earth structure from electrical resistivity tomography survey

The Electrical Resistivity Tomography (ERT) method is a geophysical prospecting technique for determining subsurface structure in terms of electrical resistivity distribution. Direct current is injected into the ground through a pair of electrodes, and the potential difference is measured using another pair of electrodes. The estimated resistivity model of the subsurface is then obtained using a mathematical optimization algorithm called the inversion algorithm, which incorporates multiple measured potential differences from different electrode configurations as the input data. The inverted resistivity model serves as a resource for the interpretation process of the survey. Specialists employ the model and the prior geological information in the area to extract the subsurface geological structure under the data measurement profile. The inverted model can be treated as a two-dimensional image in which each element represents resistivity. The image can be visualized as a blurred or distorted version of the actual resistivity image of the subsurface. We, therefore, developed a post-inversion image enhancement code using a neural network aiming to recover the true subsurface model with predetermined features. We employed the convolutional neural network (CNN) that uses the inverted models as input and returns an enhanced model as output. We tested our developed neural network with a case study that utilized the proposed method to recover the layered earth structure which is often found in real surveys. The electrode spacing was 5 meters in the Schlumberger array configuration. The true subsurface resistivity models of training data and validating data for evaluating the neural network were randomly generated based on the predetermined feature of the layered structure. We then generated their respective inverted models from those data through simulated inversion routine. As a result, 94.75% of the enhanced models in the validation dataset exhibited a lower loss metric compared to the original inverted models in the same validation dataset. We also applied the proposed method to practical field data to recover the subsurface layers and compared them with stratigraphic information from a borehole in each area. The result showed that the proposed method gives well-resolved structures in the enhancement process after the typical inversion.

The Application of Rayleigh Wave Method in the Underground Void Area Exploration

Underground voiding refers to the phenomenon that abnormal looseness, plate breakage, increase in porosity of underground medium lead to the formation of voids that decrease the stability of stratum and weaken the physical and mechanical properties. For example, road underground voiding will seriously affect the comfort and safety of vehicle driving. At present, the engineering geophysical prospecting technology is mainly used to detect the void area. In this paper, the elastic wave simulation method is used to study the response of the Rayleigh wave method to the underground void of the pavement. The response regularity is explored by adjusting the model parameters. The outdoor experiment is carried out according to the law parameters, and the effectiveness of the elastic wave for the detection of shallow surface voids is verified.

Characterization of a Small Abandoned Municipal Solid Waste Scattered Landfill Combining Remote Sensing and Near-Surface Geophysical Investigations

This study reports the combination of remote sensing and ground geophysical techniques to locate an abandoned and hidden municipal solid waste landfill located in a fluvial plain in the French Western Alps. Following earthworks and further floods that eroded into the river bank, wastes made of a mixture of plastic, metal and soil/earth, were uncovered and some of them flowed into the river. The existence of an abandoned landfill, several decades-old, was known, but the knowledge of its exact location was forgotten. Historic aerial photographs back to 1948 allowed delineation in space and time of the location of a platform that was used for landfill operations between around 1973 and 1983. A LiDAR DEM acquired in 2012 allowed was used to locate topographic depressions 0.1 to 0.4 m in depth, notably inside the platform. These depressions are interpreted as resulting from differential compaction originating from the presence of compressible wastes. Geophysical mapping techniques (magnetic and electromagnetic) confirmed the presence of anomalies inside the identified platform. Geophysical imaging techniques (ground-penetrating radar, electrical resistivity tomography) provided a quantitative evaluation of the width and depth of the individual pits. The combination of the different techniques allowed for estimating the first-order volume of waste. The methodology adopted in this work is applicable to detect landfills exhibiting differential compaction and physical contrasts.

Integrated geophysical methods used to explore geothermal potential areas in Siogung-Ogung, North Sumatra, Indonesia

The manifestations of some hot springs in Siogung-Ogung, North Sumatra, Indonesia have increased speculation of likely geothermal sources. Therefore, integrated geochemical and geophysical methods were employed to identify the geothermal prospect of the area. Two-dimensional electrical resistivity and geomagnetic methods were used for the geophysical survey. The geochemical survey used three concentration measurements: geothermometer silica (SiO2), geothermometer Na-K, and geothermometer Na-K-Ca. A Wenner Schlumberger array with a 5-meter electrode spacing was used to acquire the 2-D resistivity data, which was processed using Res2Dinv software. The geomagnetic method was performed with a proton precession magnetometer, and the data were processed using Surfer to produce the magnetic residual map. The 2-D electrical resistivity results show that the area has low resistivity values (1-700 Ωm). The resistivity values from 1 to 100 Ωm could be due to the presence of hot waters in alluvium, and the resistivity values &gt; 400 indicate andesite rock, which can function as a hot water conductor from the source. The magnetic residual map shows geomagnetic values from 150 nT to 360 nT, which infer the potentiality of geothermal within the study area. The geochemical results show that the reservoir temperature is 572 °C. Based on the integrated results, the study area has promising geothermal potential.

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.