Geophysical Tools Research Articles

Magnetometric Surveys for the Non-Invasive Surface and Subsurface Interpretation of Volcanic Structures in Planetary Exploration, a Case Study of Several Volcanoes in the Iberian Peninsula

Volcanoes are typical features of the solar system that offer a window into the interior of planets. Thus, their study can improve the understanding of the interiors and evolution of planets. On Earth, volcanoes are monitored by multiple sensors during their dormant and active phases. Presently, this is not feasible for other planets’ volcanoes. However, robotic vehicles and the recent technological demonstration of Ingenuity on Mars open up the possibility of using the powerful and non-destructive geophysical tool of magnetic surveys at different heights, for the investigation of surfaces and subsurfaces. We propose a methodology with a view to extract information from planetary volcanoes in the short and medium term, which comprises an analysis of the morphology using images, magnetic field surveys at different heights, in situ measurements of magnetic susceptibility, and simplified models for the interpretation of geological structures. This methodology is applied successfully to the study of different examples of the main volcanic zones of the Iberian Peninsula, representative of the Martian intraplate volcanism and similar to Venus domes, as a preparatory action prior to the exploration of the rocky planets’ surfaces.

Contribution of Ground Penetrating Radar in the study of an amazon tide channel, influenced by macro tide

This article shows the Ground Penetrating Radar (GPR) experiment applied in the Urumajó tidal channel (Augusto Côrrea, Pará, Brazil) that flows into the Caeté river estuary (Atlantic Ocean). This tidal channel has a length of 50 km (source - mouth, near Augusto Côrrea city) and a hydrographic basin of 544 km2. The GPR geophysical tool allowed extracting information under the depth of the channel bed in the various 2-D profiles. In the central part of the tidal channel, sediment accumulations were identified probably due to the influence of the tide. The results show that with the 200 and 400 MHz frequency antennas, the GPR is able to obtain records (radargrams) of the channel bed, over 7,5 m deep. During the rainy season, the tidal channel is covered by sand (30%) and mud (70%), however, in the dry season the muddy granulometric class (72%) increases a little and the sand (28%) decreases, sediments sludge predominated on the banks of the channel and increased upstream. The silting up of the tidal channel is a consequence of several activities carried out on the banks of the channel (livestock, agriculture, housing, ports, etc), resulting in deforestation.

Three-Dimensional Inversion of Semi-Airborne Transient Electromagnetic Data Based on a Particle Swarm Optimization-Gradient Descent Algorithm

Semi-airborne transient electromagnetics (SATEM) is a geophysical survey tool known for its ability to perform three-dimensional (3D) observations and collect high-density data in large volumes. However, SATEM data processing is presently restricted to 3D model-driven inversion, which is not conducive to detailed surveys. This paper presents a new 3D model- and data-driven inversion algorithm using the particle swarm optimization (PSO) and gradient descent (GD) algorithms. PSO is used to suppress the multiplicity of solutions associated with inverse problems, and the GD algorithm is employed to accelerate the convergence of the inversion process. For the PSO-GD algorithm, a new model-updating equation is established and a cosine probability function is introduced as a weighting term for PSO and GD algorithms to ensure a smooth transition between the two algorithms in the iterative process. The α-trimmed filter function is used as a regularization constraint to smooth the model. The stability and reliability of the PSO-GD algorithm are verified through numerical simulations. Finally, the new algorithm is applied to the processing of SATEM measurements of the Qinshui coal mine in Jincheng, Shanxi Province, China.

Locating Graves in Different Soil Types and Burial Ages in Pulau Pinang using Ground Penetrating Radar

Ground-penetration radar (GPR) is a geophysical tool widely applied in archaeological and forensic research, such as identifying the exact position of graves. A detailed GPR survey was conducted on the cemeteries in Permatang Pasir and Titi Teras, Penang Island. Moving a 500MHz GPR antenna along parallel transects inside grids was used to collect data. The study’s aim was to present two case studies with varying soil types and burial ages. Analysis of reflection shape, reflection strength and signal polarity helped in the interpretation of burial anomalies. The results varied depending on the soil type; in the sandy field, the GPR investigations were clearer and less complicated than in the clayey sand field. When the conditions are ideal (low conductivity areas with little vegetation), GPR provides highly informative and precise results. Time-slices representations were used as a method to provide details about the subsurface reflection at a certain depth.

Investigating groundwater recharge potential of Notwane catchment in Botswana using geophysical and geospatial tools

Study regionThis study is conducted over the Notwane Catchment Area (NCA) in Southeastern Botswana using geospatial and geophysical tools. Study focusGeospatial and geophysical tools, which provide spatial information for both the surface and subsurface have been widely used in groundwater exploration because of their capability in detecting physical properties that are related to groundwater phenomena. In this research, relevant remotely sensed data including aeromagnetic data and satellite images were used to identify potential groundwater recharge zones within the NCA as a contribution towards improved water resources management amid the changing climate. The multi-disciplinary approach used could offer a more reliable way to identify potential recharge zones, particularly in semi-arid hard rock terrains. New hydrological insights for the regionAssessment of groundwater recharge potential looking at remotely sensed data revealed that built-up areas expanded significantly between 2009 and 2019 with implications for run-off and flooding. Through aeromagnetic data interpretation of Euler deconvolution solutions and apparent susceptibility computations, weathered zones and geologic lineaments, mainly dykes and faults, indicating areas with increased secondary porosity were identified. Consequently, the groundwater recharge optimization model was used to determine areas with higher recharge potential which lie on the central part of the NCA, northeastern margin and the southernmost part bounded by topographical relief of hills with thick vegetation. These areas are characterized by approximately 200 m depth of weathering and predominantly east-west structural features.

Electrical and electromagnetic responses over steel-cased wells

Electrical and electromagnetic (EM) methods can be diagnostic geophysical imaging tools for monitoring applications, such as carbon capture and storage or hydraulic fracturing. In these settings, it is common that steel-cased wells and other steel infrastructure are present. Grounded source methods, which use electrodes to inject current into the earth, are of interest for casing integrity and monitoring applications. Electrostatic, or direct current (DC) resistivity, experiments form the basis of our understanding of the physics of grounded source experiments in terms of charges, currents, and electric fields. Steel-cased wells are highly conductive, and although their presence makes numerical modeling more challenging, they can help targets of interest be detected because they channel charges and currents to depth. Time-domain EM experiments use a time-varying transmitter current. Understanding the EM response requires that we consider both galvanic, or DC, currents as well as image currents that are induced in the subsurface. As compared to DC experiments, the physics of EM is more complex because of the multiple current systems as well as the need to consider magnetic permeability of steel-cased wells. However, EM experiments have the advantage that they can provide a large data set that is sensitive to a target of interest. Ultimately, this will increase the potential for being able to extract information about the target.

Geophysical tools to study the near-surface distribution of the tailings in the Smaltjärnen repository, south-central Sweden; a feasibility study

Geophysical tools to study the near-surface distribution of the tailings in the Smaltjärnen repository, south-central Sweden; a feasibility study

NVESTIGATION OF SALINE WATER INTRUSION IN SELECTED COASTAL AREA OF RIVERS STATE, SOUTH-SOUTH NIGERIA

The study was aimed to investigate the intrusion of saline water in some selected areas of Rivers State Nigeria. The objectives of the present study were summarized by the use of electrical resistivity signatures of the area’s subsurface to study the occurrence of Saltwater-freshwater interface, determining the depth and thickness of different subsurface layers for groundwater exploitation and delineate saline-water intruded sands in the study area using the borehole geophysical logging tool. The study scoped at producing geologic maps of the study area to gather information concerning the geomorphologic features, application of the electrical resistivity method (VES) to obtain necessary data to investigate the occurrence of seawater intrusion by determining the resistivity, depth and thickness of the various lithologic layers and delineating saline-water intruded sands in the study area by exploring the potential of borehole geophysical logging tool. A total of 11 geoelectric (VES) surveys and four (4) downhole logging was carried out in selected locations within the River State Metropolis to investigate the saline water intrusion in the area. The obtained results reveal that from the Electrical resistivity sounding, the predominant lithologies in the area includes clay, clayey sand, coarse sand, consolidated sand, gravelly sand, consolidated gravel sand, gravelly sand, silty sand, freshwater bearing sand and saltwater bearing sand. Geoelectric layers identified across the area ranged from 3 to 6 layers. Resistivity ranged from 29.60 to 364058.00 Ohm.m for lithologic units, 113 to 181 Ohm.m for freshwater sands and 0.11 to 28.50 Ohm.m for saline water sands. Resistivity field type curves recognized included; H, QQ, AA, KHA, QH, HKH, QQHK, A, HK, KHK and KQH depicting the heterogenous nature of soils in the area. Six of eleven VES points encountered salt water at varying depths and include; Ogonokom, Eagle Island, Okirika, Assarama, Ikuru and Opobo sounding points. Thickness of the saline sandy layers ranged 3.10 m to 71.48 m. Downhole logging (SP and Resistivity) conducted in four coastal communities of the study area revealed four lithologic units which includes clay, clayey sand, coarse sand and saline water bearing sand. Saline zones were identified as having negative SP values and low resistivities. Clay were mapped as areas having positive SP values and low resistivities. The thickness of the saline zones ranged from 16 to 74 m. The largest saline layer thickness was obtained at Bonny. This study has shown that boreholes in Bille and Bonny communities exceeding depths of 15 m are likely to encounter salt water. The saltwater intrusion is predominantly concentrated around the southern part of the study area around Bonny and Opobo communities. The presence of Opobo River, Bonny River and a suite of creeks which are open to the Atlantic Ocean area responsible for the salt intrusion into these coastal boreholes. The outcome of the study yielded the importance that boreholes in Bonny, Opobo and Bille communities that has encountered saline water should be prevented from further use until treatment for salt water intrusions are conducted and water exploitation plan should be developed by the government and enforced to be utilized by residents in Buguma, Degema, Abonnema and NLNG to prevent saline intrusion because these communities are the most vulnerable to saline intrusion from over-exploitation of freshwater in the area.

Electromagnetic Induction Measurements for Investigating Soil Salinization Caused by Saline Reclaimed Water

This paper focused on the use of electromagnetic induction measurements in order to investigate soil salinization caused by irrigation with saline reclaimed water. An experimental activity was carried out during the growing season of tomato crop in order to evaluate expected soil salinization effects caused by different saline agro-industrial wastewaters used as irrigation sources. Soil electrical conductivity, strictly related to the soil salinity, has been monitored for three months by means of Electromagnetic Induction (EMI) measurements, and evident differences in the soil response have been observed. The study highlighted two aspects that can improve soil investigation due to the utilization of geophysical tools. First, EMI data can map large areas in a short period of time with an unprecedented level of detail by overcoming practical difficulties in order to massively sample soil. At the same time, repeated measurements over time allow updating real-time soil salinity maps by using accurate correlations with soil electrical conductivity. This application points out how integrated agro-geophysical research approaches can play a strategic role in agricultural saline water management in order to prevent soil salinization risks in medium to long-term periods.

Tree root imaging by electrical resistivity tomography: geophysical tools to improve understanding of deep root structure and rhizospheric processes

Tree root imaging by electrical resistivity tomography: geophysical tools to improve understanding of deep root structure and rhizospheric processes

Multifrequency electromagnetic geophysical tools for evaluating the hydrologic conditions and performance of evapotranspiration barriers

Surface barriers are designed to isolate subsurface contaminants for 1000 years or longer, functionally limiting water infiltration and removing the driving force for contaminant transport to groundwater. Cost-effective monitoring is challenging because of the long design life for surface barriers, spatial limitations and finite lifetime of in situ sensors, and performance metrics related to drainage. Hence, ground-penetrating radar (GPR) and electromagnetic induction (EMI) tools were evaluated for use in performance monitoring of surface barriers. GPR and EMI were used to non-invasively interrogate the Prototype Hanford Barrier (PHB), an evapotranspiration-capillary break barrier established in 1994 at the Hanford Site, in southeastern Washington State. Both geophysical methods were evaluated for providing indirect estimates of subsurface moisture content conditions that were compared to point scale measurements from borehole neutron logs. Surveys were performed during characteristically wet and dry periods to observe a range of hydrologic states of the barrier soil. Although EMI surveys were expected to show seasonal changes associated with changes in the bulk conductivity of the barrier soil layers, the effectiveness of the method was limited by the effects of metallic infrastructure embedded in the barrier. GPR estimates of volumetric water content were typically within 2–3% of the highest water contents from neutron probe measurements for both wet and dry periods, providing reasonable estimates of water content. Given that PHB monitoring data over the past 25 years has demonstrated its success in limiting deep drainage, GPR was found to be a cost-effective method for demonstrating continued barrier performance, with a greater capacity to quantify moisture content distributions over much larger areas relative to point measurements.

Hydrogeothermal potential assessment in a complex tectonic environment by geophysical and hydrogeochemical tools: a case of the geothermal province of Hajeb Layoun-Jilma-Oued Hjal basins (Central Tunisia)

Hydrogeothermal potential assessment in a complex tectonic environment by geophysical and hydrogeochemical tools: a case of the geothermal province of Hajeb Layoun-Jilma-Oued Hjal basins (Central Tunisia)

Geophysical characterisation of geologic features with mining implications from ERT, TDEM and seismic reflection (Mining District of Linares-La Carolina, Spain)

In this study, the effectiveness of different geophysical techniques is analysed in relation to the imaging of geological structures with mining interest. To achieve this goal, the old district of Linares-La Carolina (Southeast Spain) is chosen due to the presence of dense swarm of mineralised dykes, primarily consisting of galena (PbS). In particular, the western boundary of the mining district is studied. At this westernmost area the veins lose their continuity due to regional fractures which resulted in the abandoning of the extracting labours.Direct information from both the surface geology and several boreholes are used as ground-truth calibration and verification for the geophysical tools used in this study.The seismic response is characterised by high-amplitude reflectors, generally at the base of the sedimentary cover. The seismic profiles suggest lateral changes in the thickness and the existence of fractures affecting the sedimentary cover and/or the top of the acoustic basement. However, this technique has proved ineffective when studying the Palaeozoic substrate, precisely at those areas where the veins are hosted.Electrical resistivity tomography (ERT) studies suggest fractures and lateral changes in the facies, in both the sedimentary cover and the Palaeozoic basement. The basement shows phyllites in the granite intrusion, which are crucial for the elastic properties of the hosting rock and therefore indicate areas prone to further mineralisation. Time-domain electromagnetic (TDEM) data, which is an excellent complement to the two previous techniques, have also been collected. Data have been taken with different configurations and varying measurement parameters at each sounding station. This approach has made it possible to compare the effectiveness benefits and drawbacks of the different methods.

Geotechnical and geophysical characterisations of construction waste-infilled quarry for housing and commercial developments: Case study of Tehran, Iran.

The fast population growth in the metropolitan areas of the province of Tehran has led to the scarcity of land and inevitable expansion of urban construction to non-engineered fills and construction/demolition waste disposal sites. An abandoned aggregate quarry, infilled with construction wastes over 16 years, has been recently selected for a new development project consisting of several multi-storey commercial and residential complexes (up to 7 storeys). This study was aimed at delineation of the waste materials, geophysical and field and laboratory geotechnical characterisations prior to foundation design, and the design of the excavation programme. Geo-electric resistivity test was used to delineate the waste materials from natural ground materials. Surface and downhole P- and S-wave velocity measurements were used for the estimation of dynamic elastic properties of the wastes. In total, 12 boreholes (15-30 m deep) along with 10 test pits (4-8.5 m deep) provided the opportunity for visual observations of the waste materials, necessary sampling for compositional analyses, laboratory shear strength tests and determination of waste deposit thickness in different regions of the site. Manual standard penetration test (SPT) was also used to evaluate in situ stiffness of the fine materials of the waste. Six field plate load tests were performed on the waste materials at their natural water content conditions and at saturated (flooded) ground conditions to determine their compressibility and the ground reaction modulus. Based on the results from extensive characterisation programme, it was concluded that the waste materials are in a metastable state and exhibit heterogeneity across the site. The findings of current case study can provide new insight into construction/demolition waste behaviour, using available geophysical and geotechnical tools and testing procedures for characterisation, and eventually helping in reliable design of foundations for new development projects.

Review of Applications of Ground Penetrating Radar as an NDT Tool

Ground-penetrating radar (also referred to as GPR, ground probing radar, or georadar) is a near-surface geophysical tool with a wide range of applications. Over the past 30 years, GPR has been used successfully to aid in constraining problems in diverse fields such as archaeology, environmental site characterization, glaciology, hydrology, land mine/unexploded ordinance detection, sedimentology, and structural geology. In many cases, however, GPR surveys have been planned or executed with little or no understanding of the physical basis by which GPR operates and is constrained. As a result, many unsuccessful GPR studies have also been presented or published over the past 30 years. The objectives of this primer are to (1) provide an introduction to the important variables pertinent to GPR and (2) explain the relevant aspects of these variables in GPR acquisition, in an attempt to provide fundamental knowledge for improving GPR usage in the future.

Machine learning based approach for the interpretation of engineering geophysical sounding logs

In this paper, a set of machine learning (ML) tools is applied to estimate the water saturation of shallow unconsolidated sediments at the Bátaapáti site in Hungary. Water saturation is directly calculated from the first factor extracted from a set of direct push logs by factor analysis. The dataset observed by engineering geophysical sounding tools as special variants of direct-push probes contains data from a total of 12 shallow penetration holes. Both one- and two-dimensional applications of the suggested method are presented. To improve the performance of factor analysis, particle swarm optimization (PSO) is applied to give a globally optimized estimate for the factor scores. Furthermore, by a hyperparameter estimation approach, some control parameters of the utilized PSO algorithm are automatically estimated by simulated annealing (SA) to ensure the convergence of the procedure. The result of the suggested ML-based log analysis method is compared and verified by an independent inversion estimate. The study shows that the PSO-based factor analysis aided by hyperparameter estimation provides reliable in situ estimates of water saturation, which may improve the solution of environmental end engineering problems in shallow unconsolidated heterogeneous formations.

Selenium mobility in a major Chalk aquifer (Lille metropolis, northern France): Contaminants cycles driven by geology, redox processes and pumping

Chalk groundwater in northern France presents selenium (Se) concentrations from <10 to 70 μg L−1, partly exceeding the latest European Framework Directive's drinking-water limit value of 20 μg L−1. Better to understand the heterogeneous dynamics of Se, we used a combination of geochemical, isotopic and geophysical tools on a study site belonging to the Metropolis of Lille, France. This approach provided a fine understanding of the Se fate in a dynamic redox system constrained by geology, related redox processes and pumping, illustrating how local versus global controls affect the Se cycling. A remarkable redox sequence controls element transfers in groundwater with a progressive creation of reductive conditions. Highlighted by geophysical tools, a wide fracture corridor in the Chalk formation disrupts the geological setting of this redox sequence. Under pumping, this corridor allows the mixing of oxygenated groundwater with groundwater under reducing conditions. The evolution of isotopic compositions of sulphate molecules confirms the global reduction trend of sulphates, while pyrite oxidation occurs very locally, together with high Se concentrations. Pyrite is expected to play a predominant role in Se mobility in the Chalk aquifer. Se and other redox sensitive elements (Fe, Mn, N and S) undergo multiple redox cycles, resulting in a Se-rich redox front that migrates downward over time within the water-level fluctuation zone of the porous Chalk. With the decreasing trend of water levels caused by global changes, a Se stock could be immobilized in the unsaturated zone, but nitrate content and redox conditions in the saturated zone will be major drivers for Se mobility.

GPR for earth and environmental applications: Case studies from India

Ground Penetrating Radar (GPR) is widely applied for rapid and precise mapping of the near surface structures. We performed GPR survey using Terra Sirch-3000 single channel control GPR meter with 2D data collection for civil engineering, environmental, archeological, geological features, aquifer contamination and seawater intrusion studies in Indian context. The 200 MHz and 400 MHz frequency antennae with adjusted dielectric constant, scans per unit, range, transmit rate, gain points, and filters were used for attaining the targets depth up to 3–8 m. The collection of GPR data was on Geologic Scan, Utility Scan, Structure Scan, and Terra SIRch modes with resolution of 16 bits, and was processed in RADAN (version 5.0) using various options to get clear anomaly of the targets. Based on the targets, the scanned images were verified with excavations, electrical resistivity tomography, and soil and water chemistry which were complementing with the GPR anomalies. Results demonstrated in this article are, 1) identification of caving in trenchless MS pipe of 1700 mm diameter with feasibility for trenchless technology, 2) discovery of ancient temple, 3) deciphering a subsurface intrusive body (i.e. dolerite dyke), 4), detection of clandestine pipes, 5) demarcating fresh groundwater zones within industrial clusters, and 6) identification of seawater intrusion in coastal area. The study establishes that the GPR works as rapid tool in unraveling shallow subsurface complexities with high-resolution images and offers a geophysical tool for wide range of earth and environmental management.

Novel methodology for interpretation of magnetic anomalies due to two-dimensional dipping dikes using the Manta Ray Foraging Optimization

The high rate of depletion of mineral resources in different parts of the World has prompted researchers to intensify their search for new deposits. These searches are usually conducted using different geophysical tools and algorithms. The potential and efficacy of adapting the bioinspired Manta rays foraging optimization algorithm (MRFO) as a tool for estimating model parameters of a two-dimensional dyke-like magnetic profile anomalies are investigated. The process of implementing the MRFO algorithm in accurate estimation of four distinctive model parameters- amplitude coefficient, inclination, halfwidth and depth of burial from the surface, of an infinitely dipping dyke was presented. The experimental data comprise synthetically generated magnetic anomalies that were later corrupted with noise at levels of 5, 10, 15 and 20%, and finally, case examples from two mining sites in Peru and China. The algorithm was fast, stable and consistent in its search for the global best solution to each of the geophysical inverse problems, which all terminated before the 1000 iterations fixed for it to do so. Its performance was excellent even in the presence of random noise with varying levels. Thus, the MRFO procedure is accurate and reliable procedure for solving geophysical inverse problems and is recommended for use in modelling other geophysical problems like vertical electrical sounding, gravity, self-potential and magnetotelluric data.

Two-dimensional magnetotelluric finite element modeling by a hybrid Helmholtz-curl formulae system

The magnetotelluric (MT) method is an important geophysical electromagnetic induction exploration tool, with proper inversion routines, we can image the electrical conductivity structures of the Earth. A reliable inversion routine needs to iteratively call forward modeling solvers which solve the electromagnetic induction equations in the Earth. In this study, a novel hybrid Helmholtz-curl formulae system is presented for two-dimensional (2D) MT finite element modeling. In the air space with small values of conductivities, the well-behaved Helmholtz equation is used to represent the propagation of the electromagnetic field. In the Earth domain with positive values of conductivities, the well-behaved curl-curl electromagnetic equation is used to represent the inductive and propagating behaviors of the electromagnetic field. On the air-Earth interface, with arbitrary surface topographies, continuity conditions of the electromagnetic fields are enforced to guarantee the solution's uniqueness. Several synthetic models with both simple and complex geo-electrical structures incorporating topographies are used to verify and test the performance of the newly developed hybrid Helmholtz-curl formulae system. Numerical tests show that the hybrid Helmholtz-curl formulae system is numerically stable when using low conductivity values in the air space and using low signal frequencies. The hybrid Helmholtz-curl formulae system is an alternative algorithm to develop 2D MT forward modeling solvers.