Resistivity Zone Research Articles

Electrical resistivity imaging for detection of hydrogeological active zones in karst areas to identify the site of mining waste disposal.

Hydrogeological active zones found in mine waste (tailings) dumping sites are a major source of concern that threatens the safety of the environment and groundwater, especially in karstic areas. Therefore, detecting and identifying these regions correctly will help in selecting the appropriate sites for tailings disposal and avoid consequential environmental problems. In this study, electrical resistivity imaging (ERI) surveys with high-resolution data were carried out to detect hydrogeological active zones in an area proposed as a settling pond for mining tailings accumulated from El Mochito mine property, located in the north-western section of Honduras. Two-dimensional (2-D) inversion results of thirty-four survey lines revealed several zones of low resistivity. These zones indicate water-/clay-bearing regions that are structurally weak. However, some survey lines, the limestone beneath the surface is entirely compacted; as such, it is considered to be an ideal site for tailings pond construction. In addition, on the eastern side of the valley, there is a large chunk limestone layer that is compacted and can be considered for tailings pond construction. The ERI method provided insight and developed an informative subsurface map to detect the hydrogeological active zones, thus proving it as a beneficial tool used for selecting disposal sites for mining tailings in karstic areas.

Application of electromagnetic and electrical resistivity methods for foundation studies at Ahmadu Bello University Phase II, Zaria

Very Low-Frequency Electromagnetic (VLF-EM) and 2D electrical resistivity survey were carried out at the Ahmadu Bello University Phase II in order to investigate the suitability of the soil materials for the foundation of super-structures in the study area. The Terra-Plus equipment and ABEM SAS 4000 were used for VLF-EM and resistivity data acquisition respectively. The VLF-EM Data were collected along five (5) profiles at station interval of 10 m along each profile. The data collected from each of the VLF-EM profile were processed and interpreted with the aid of Karous-Hjelt and Fraser filter software. Electrical resistivity profile was laid on the weak zones revealed by the 2D VLF-EM profiles through the aid of dipole-dipole configuration. The data obtained were processed and interpreted with the aid of Res2Dinv software. Borehole log of the study area was used as additional information which serves as a calibration tool. The 2D imaging profile of VLF-EM highly correlates with resistivity profile. The 2D VLF-EM and resistivity profiles revealed the conductive zone and resistive zones. These zones are suspected to be geological features (dyke, faults and fractures). This geological feature such as fracture zones was filled with an earth’s materials which are probably sandy clay and mottled clay, and these materials are highly undesirable for the foundation of building structures due to its characteristics of swelling and contracting during rainy and dry season respectively. Thus, undesirable materials should be excavated and be refilled with suitable materials for the foundation of super-structures and also, geological bodies should be avoided when the foundation of the structures is to be erected.
 Keyword: VLF-EM, electrical resistivity, foundation of super-structures, geological feature, undesirable materials

The effect of Bi addition on the electrical and microstructural properties of SAC405 soldered structure

Purpose This study aims to investigate the effect of bismuth addition (up to 30 Wt%) on the microstructure and electrical conductivity of a commercial lead-free alloy (SAC405) near the solder/substrate soldered joint. The system under study is referred in this work as (SAC405 + xBi)/Cu, as Cu is the selected substrate in which the solder was casted. The electrical resistivity of this system was investigated, considering Bi addition effect on the local microstructure and chemical composition gradients within that zone. Design/methodology/approach Solder joints between Cu substrate and SAC405 alloy with different levels of Bi were produced. The electrical conductivity along the obtained solder/substrate interface was measured by four-point probe method. The microstructure and chemical compositions were evaluated by scanning electron microscopy/energy dispersive spectroscopy analysis. Findings Two different electrical resistivity zones were identified within the solder interface copper substrate/solder alloy. At the first zone (from intermetallic compound [IMC] until approximately 100 μm) the increase of the electrical resistivity is gradual from the substrate to the solder side. This is because of the copper substrate diffusion, which established a chemical composition gradient near the IMC layer. At the second zone, electrical resistivity becomes much higher and is mainly dependent on the Bi content of the solder alloy. In both identified zones, electrical resistivity is affected by its microstructure, which is dependent on Cu and Bi content and solidification characteristics. Originality/value A detailed characterization of the solder/substrate zone, in terms of electrical conductivity, was done with the definition of two variation zones. With this knowledge, a better definition of processing parameters and in-service soldered electronic devices behavior can be achieved.

Self Potential untuk Pendugaan Reservoir Sistem Panas Bumi Blawan

Self-Potential methods that have advantages in providing more extensive and integrated information to better ensure that geothermal areas have potential geothermal resources. This study discusses the geothermal system in the Ijen volcano area based on the value of resistivity and potential different from the subsurface structure. The stages in the implementation of research programs are (1) literature study, carried out to obtain accurate and up-to-date information, (2) data retrieval, carried out to obtain primary and secondary data, (3) data search, data processing, and data interpretation, carried out using Res2div and Surfer software to obtain subsurface structure mapping (4), evaluation, was carried out as a monitoring of geothermal resource potential mapping research. The modeling results were obtained from the subsurface layer in Blawan geothermal manifestation consisting of 3 zones with upper resistivity zones (> 10 ohm to 50 ohm meters), reservoir zones (> 50 ohm meters to 100 ohm meters) and heat source zones (> 100 ohm meters, based on the isopotential contour map, that the Blawan region is a destructive zone.

Vertical Electric Sounding of Leachate Contaminant Plumes at a Dumpsite in Obigbo, Rivers State, Nigeria

The quality of underground water at a dumpsite in Obigbo, Rivers State, Nigeria, was investigated by collecting 7 vertical electrical soundings (VES) using Wenner electrode configuration with current electrode spacing (AB/2) ranging from 1.0 m to 300 m. Field data were acquired using the SAS 300C resistivity meter and accessories, coordinates and elevation were measured using the Global Positioning System (GPS) at each sounding station. The VES data showed that the area is composed of clay, sandy clay and sand. The contaminated zones have low resistivity and corresponding high conductivity. Two zones were identified, zones of low resistivity and high resistivity with values of 11.3 Ωm to 21.4 Ωm, and 357.0 Ωm to795.0 Ωm respectively. There is thus, both lateral and downward movement of the contaminant leachate plumes. The results also revealed that the surrounding soil and groundwater around the landfill has not been contaminated to depths exceeding 15.6 m, which is shallower than the productive aquifer depth greater than 37.0 m. Judging from the age of the dumpsite, this site has a good protecting capacity, probably as a result of the presence of sufficient confined layers of clay that have impeded or slowed down the percolation of leachate into the aquifer. The aquifer is the underlying rocks of sand and gravel that are porous which constitute the water body. Keywords : Dumpsite, Resistivity, Sounding, Leachate, Aquifer.

Geophysical responses and possible geothermal mechanism in the Gonghe Basin, China

In Qinghai Province of China, the Gonghe Basin is characterized as a potential hot dry rock (HDR) area due to the high heat flow rate and high-temperature records from several springs and drillings. However, the regional geothermal mechanism is still disputable and then essential to be discussed for the HDR exploration strategy, even for analysis in other areas. Geophysical methods are useful tools of analysing regional tectonic activities and geological structures, which are related to heat generation and conduction. In this paper, we mainly focus on the geophysical data within different scales. Firstly, we mapped the epicentral distribution along a profile covering Qinghai-Tibetan Plateau and the north part of India. This result shows that the Gonghe Basin was in a relatively stable area where less earthquake happened in deep zones (> 40 km). The geothermic mode should be thereby different from another geothermal field Yangbajain, which has a high frequency of earthquake events in deep zones (> 40 km). Secondly, we focus on the area of the Gonghe Basin and its surrounding area. By using the gravity and magnetic data, we estimated the Moho depth and Curie point depth through the Park-Oldenburg algorithm. The results indicate that the Gonghe Basin was at the gravity gradient zone without noticeable depth gap of Moho interface. The regional aeromagnetic data along with the Curie point depth was in a different trend. The high-value magnetic zone covers the major part of the Triassic igneous rock area. In this case, the heat from the deep zone (> 30 km) might not be the major contributor to the HDR forming here. Referred MT, seismic inversion results, we integrated all geophysical results. Based on this, a conceptual model in the Gonghe basin was then put forward. The low resistivity zones such as the magma capsules or melted granites in the upper-crust might be the significant heat resource for the HDR, although those from lower crust, mantle and the igneous rocks might make some contributions. The heat was conducted through the near-ground fractures and make the Gonghe Basin as a potential geothermal area, also validated by other geochemical evidence.

Application of Electrical Tomography to Put in Evidence the Thickness and Structure of the Filling of Dayet Iffer (Middle Atlas, Morocco)

The Dayet Iffer belongs to the Dayets of tectono-karst origin of the Northern Middle Atlas. After its watershed genesis of middle altitude during the Quaternary, two lacustrine formations were deposited on the surface while other thick formations exist in depth. The detailed sedimentological study of the soltanian and holocene lithological sections on the surface and the 14C datings helped recognize part of the history of the watershed. The geophysical study allowed to detect the thickness of the superficial geological formations as well as the various geological phenomena (tectonic and/or karst) that affected them from the genesis to the present. The current shape of the watershed where the Dayet Iffer exists is only the result of an evolution where sedimentary, tectonic and karst phenomena interfere. The tomography obtained with Res2DInv software, performed for the first time at the Dayet Iffer, reveals the presence of three ranges which can be interpreted as three resistive, intermediate and conductive zones with a large set of faults. These results helped determine the thickness (over 160 m) of the sedimentary filling. This shows that the hydrological behavior of the Dayet Iffer takes into account both horizontal flows at the stratification and/or karstic joints and the movement of sub-vertical fractures.

Application of Resistivity Method for Mining Tailings Site Selection in Karst Regions

Disposal of mining wastes (tailings) is one of the most severe issues related to groundwater contamination. Therefore, a properly selected disposal site helps to prevent the leakage of dissolved materials in the tailings to groundwater, especially in the karstic area. Where the karstic environment is one of the challenges facing groundwater environmental and engineering issues, for instance, groundwater exploration, vulnerability assessment, and hazard estimation. In this study, the resistivity method with a high-resolution surface data survey was carried out to investigate the pond location selection for mining tailings disposal at El Mochito mine site, northwest Honduras. The results of the two-dimensional (2-D) inversion for sixteen surveyed lines revealed that many low resistivity zones. These zones are related to water/clay-bearing zones that are structurally weak. From lines 8-12, the limestone underneath the surface is the most compact, and this is the best location in the survey area for tailings pond construction. The resistivity method has provided insight into the subsurface information and locating hydraulically conductive zones, so it can be useful for selecting the site of mining tailings.

Integration of 2D geoelectrical resistivity imaging and boreholes as rapid tools for geotechnical characterization of construction sites: A case study of New Akhmim city, Sohag, Egypt

Due to the increasing in the population density, the restriction of the agricultural areas and the scarcity of building's lands and their highly costs in Egypt, especially in Sohag province which led the officials and decision-markers to search for alternatives in the desert places to solve this problems. Therefore, New Akhmim area was proposed as a new site for constructing a new city. The main aim of this research is to delineate the engineering characteristic of the soil, identify of the bedrock depth and determine the subsurface structures and lithology of the investigated site. Great effort should be done to determine the depth to competent layer (bedrock) within the proposed site and correlate the results with the available boreholes. Complementary geophysical tool was implemented for the engineering designs in order to ensure stability of building construction and evade the shocking effects of building collapse later. Thus, electrical resistivity tomography (ERT) was undertaken on the present site for monitoring these subsurface engineering issues. The field geometry was made up of eight profiles using Wenner configuration. The data of the 2D resistivity tomography along these profiles with smallest electrode separation of 5 m were interpreted using Res2dinv software. The subsurface is characterized by three different resistivity zones, which were interpreted as gravel intercalated with coarse sands at the top, sand beneath it and shale beneath the sand layer. The ERT results were in consistent with the results of ten engineering boreholes drilling in the study area. The presence of shale was correlated to the cause of chronic differential settlements of some engineering structures like slickensides due to drying and wetting within the area. No serious structural features were detected as faults, karstification phenomena or caving. So the area is valid for construction proposes.

Delineation of leachate pathways using electrical methods: case history on a waste plaster landfill in South Korea

ABSTRACTA waste plaster landfill site, established as a high-density polyethylene (HDPE) sheet pile surrounded by a slurry wall to isolate possible contaminants within the landfill, was investigated using electric survey techniques. A sheet pile is an effective barrier wall for contaminated leachate containment, unless there are damaged zones within the pile. However, the perfect insulating properties of the pile make it difficult to apply the electrical resistivity method to measure the containment ability of the pile. To locate damaged zones in the sheet pile, which can act as pathways for the contaminated leachate, a potential difference (PD) profiling technique was applied. Through three-dimensional (3D) modelling, PD profiling demonstrated efficacy in locating damaged zones in the sheet pile. Moreover, a 3D survey was conducted to delineate the leakage pathways through the sheet pile, as well as the leachate distribution throughout the landfill. Before the 3D inversion of measured resistivity data, erroneous data caused by the sheet pile were rejected to minimise distortion of the inversion results. 3D inversion showed the sheet pile to be highly resistive overall, especially at shallow depths; however, further inspection via PD profiling identified several areas of damage in the pile. These damaged zones from PD profiling coincided well with the low resistivity zones present near the surface in the 3D inverted image. Furthermore, major leaks were found below the burial depth of the sheet pile. Thus, it was demonstrated the PD profiling and 3D resistivity survey can locate damaged zones in the sheet pile and delineate leakage pathways over the landfill site.

Piping process: Genesis and network characterization through a pedological and geophysical approach

Piping is a soil erosion process initiated by concentrated subsurface water flow, which can develop in both natural and anthropogenic landscapes and causes various environmental impacts. The piping process acts as a relief modifier, leading to soil subsidence on a short time scale. This paper aims to provide a more comprehensive characterization of the piping process in a tropical forested area of Brazil. First, we sought to understand and examine the subsurface environment of the soil, using field description and soil sampling for chemical and physical analyses (pH, CEC, bulk density, total porosity, flocculation degree). Based on this information, we performed geophysical tests using Direct Current resistivity method (DC resistivity), with six lines of electrical resistivity tomography (ERT), to map the pipes and check the connection between subsurface tunnels. Data on the basic properties of the soil aided our interpretation of the geophysical results and the genesis of the piping process. The soil of the study area presented horizons in which textural variations accompanied changes in total porosity, bulk density and flocculation degree. The DC resistivity method efficiently detected the pipes (resistive zones of values >4000 O.m and high contrast with adjacent zones) and revealed the connection and continuity of the pipe network. While various factors may contribute to the subsurface erosive process in the study area, the decisive factor triggering the process seems to be the presence of a permeable layer that lies just above the impermeable layer, which may stop water infiltration and facilitate the lateral water movement.

3D Interpretation of Resistivity Data for Groundwater Potential Assessment of Pakhli Plain, Mansehra District, Pakistan

Abstract The present research describes a method of combining geostatistical analysis with geophysical inversion of electrical resistivity data conducted in Pakhli Plain, northwestern Himalayas, Pakistan. The raw data has been collected from the Technical Report VII-I on Ground Water Resources in Pakhli Plain, Mansehra District. Subsequently, the data has been deciphered and broadened from one dimensional resistivity data into a 2D model that can be entirely visualized and deduced in a spatial sense. Interpretation and calibration of the electrical resistivity curves with the lithologies and geophysical logs of boreholes suggests possible identification of distinctive sedimentary accumulations occurring within the Pakhli Plain. The 2D and 3D gridding and visualization is imperative to map the extents of the alluvial deposits within the Pakhli Plain formed during the periods of extreme tectonic activity. The coarser sediments are associated with lower levels of resistivity as measured in the electrical surveys, whereas the finer sediments exhibit characteristically lower resistivities. Therefore, the zones of low and high resistivity values are indicative of particles associated with coarser and finer sediments, respectively. It has been mentioned that the Pakhli Plain has remained a lacustrine zone during some time in the geological past as indicated by low resistivities representing finer sediments in the middle of the Plain. Consequently, the overall transmissivity of the sediments is low, which imply poor conditions for commercial groundwater production in the Pakhli Plain. Moreover, high resistivity zones of coarse material could be further investigated for groundwater potential areas. In particular, the prime objectives of the present study include 3D modeling of underground resistivity and its exploration in terms of groundwater potential on the basis of distribution of low resistivity zones.

The Effect of Hurricane Irma Storm Surge on the Freshwater Lens in Big Pine Key, Florida using Electrical Resistivity Tomography

Animals and plants on low elevation oceanic islands often rely on a thin lens of fresh groundwater and this lens is vulnerable to seawater contamination from storm surge. Documentation of the impact of the storm surge on the freshwater lens and its subsequent recovery is limited. In September 2017, Hurricane Irma made landfall in the Florida Keys as a category 4 storm with storm surge heights in excess of 2 m. This study used Electrical Resistivity Tomography (ERT) to investigate the effect of the storm surge on the freshwater lens of Big Pine Key, FL. The study compared ERT images along three profiles ranging between 220 and 280 m length collected in 2011 with post storm data collected about 3 to 4 months (November 2017/January 2018) and eight (May 2018) months after Irma. The post storm data documented that the storm surge impacted the freshwater lens on all three profiles with low resistivity (i.e., high salinity) zones in the upper 2 m of the groundwater. The increase in salinity was most pronounced in the lower elevations of the profiles. The May 2018 data were collected immediately after 2 weeks of intense precipitation. These data showed 40% recovery of the freshwater lens, most pronounced in the lower elevation of the profiles. This suggests that both the impact of storm surge and the freshwater recovery due to precipitation are most pronounced in low elevation regions where both saline and freshwater can collect at the surface.

Study of Generation and Underground Flow of Acid Mine Drainage in Waste Rock Pile in an Uranium Mine Using Electrical Resistivity Tomography

Mineral exploration is often associated with the generation of environmental liabilities, whose potential damages might imperil local water quality. An example of these environmental impacts is the acid mine drainage—AMD, caused by sulfides oxidation and production of acid and saline effluents. The analysis of critical areas with generation and spread of contamination plumes becomes more feasible due to the possibility to obtain geophysical models of water systems, especially to identify regions with accumulation of reactive minerals and preferential water flows. The rock-waste pile named BF-04 fits in this context of contamination, and it was studied based on the Electrical Resistivity Tomography technique, inversion models and isosurface models, providing conditions to recognize sulfide zones (> 10.1 mV/V), whereas chaotic high salt content underground flows, along several depths, were identified by low resistivity zones (< 75.8 Ω m). The complex behavior of groundwater flow in this kind of artificial granular aquifer is caused by its granulometric and lithologic heterogeneities, and compacted material. In addition, the results reveled a substantial water infiltration from Consulta creek, however the most critic zones for AMD generation are located at shallow levels where the waste rock material is more exposed to atmospheric O2 and meteoric water infiltration. The bedrock was not associated with significant low resistivity anomalies, which means that its contribution to AMD generation was considered relatively less important. The results will contribute to the environmental remediation management and also to demonstrate the potential applicability of geophysical methods in mining wastes.

A scalar-geometric approach for the probable estimation of the reserve of some Pb-Zn deposits in Ameri, southeastern Nigeria

The Cretaceous sedimentary sequence of the Asu River Group in Ameri, southeastern Nigeria play host to lead-zinc ore deposits in irregular mineralized veins of non-uniform geometry. Two deposits (designated DEPOSIT A and DEPOSIT B) were economically assessed using an integrated approach. This was performed by employing a geometry-based classical scheme involving the mathematical relationship between the three cardinal variables of ore reserve estimation namely: surface area, thickness and density. Firstly, detailed and extensive geological mapping was carried out to establish the geological attribute of the mineral deposits. Since reserve estimation extends beyond exposed faces, spontaneous potential traverse, vertical electrical sounding and horizontal profiling, being orthogonal to the trend of the enclosing veins were used to characterize the existing sub-surface stratification and create forward models that revealed the concealed ore geometry (limiting depth, lateral extents and thickness variations). Subsequent to delineation, the depth to the top of the target ore lodes was obtained by implementing the Peter's half slope technique on self-potential curves. Thickness values of the ore bodies of interest were applied in three numerical classical integration techniques, i.e. Trapezoidal, Simpson's and Simpson's third-eight rule, for volume estimation. To overcome the non-uniqueness problem of DC resistivity data interpretation, the available drilling data was applied. Samples retrieved from each lode were subjected to mass and volume analysis using the CS200 electronic balance and water displacement technique, to determine the average density of each lode. Results from 2D subsurface resistivity sections showed the lead-zinc deposits as zones of low resistivity in a background of high resistivity. The 1D stratigraphic models reveal a mean thickness estimate of 11.85 m and 10.50 m for DEPOSITs' A and B, respectively. Sample densities correlate well with the average density of pure galena. Applying the scalar-geometric rule, a combined estimate of 10,778.95tonnes was obtained, representing a relatively economically viable quantity worthy of medium scale extraction. • An integrated approach to the quantitative evaluation of some Pb-Zn deposits is discussed. • Arithmetic alliance between the three cardinal variables of ore reserve assessment is employed. • To validate the result of geophysical schemes, drilling information is applied. • Ore bodies are characterized by low resistivity values. • Evaluated deposits proved fairly viable sequel to qualitative analysis.

Imaging the magmatic system beneath the Krafla geothermal field, Iceland: A new 3-D electrical resistivity model from inversion of magnetotelluric data

SUMMARY Krafla is an active volcanic field and a high-temperature geothermal system in northeast Iceland. As part of a program to produce more energy from higher temperature wells, the IDDP-1 well was drilled in 2009 to reach supercritical fluid conditions below the Krafla geothermal field. However, drilling ended prematurely when the well unexpectedly encountered rhyolite magma at a depth of 2.1 km. In this paper we re-examine the magnetotelluric (MT) data that were used to model the electrical resistivity structure at Krafla. We present a new 3-D resistivity model that differs from previous inversions due to (1) using the full impedance tensor data and (2) a finely discretized mesh with horizontal cell dimensions of 100 m by 100 m. We obtained similar resistivity models from using two different prior models: a uniform half-space, and a previously published 1-D resistivity model. Our model contains a near-surface resistive layer of unaltered basalt and a low resistivity layer of hydrothermal alteration (C1). A resistive region (R1) at 1 to 2 km depth corresponds to chlorite-epidote alteration minerals that are stable at temperatures of about 220 to 500 °C. A low resistivity feature (C2) coincides with the Hveragil fault system, a zone of increased permeability allowing interaction of aquifer fluids with magmatic fluids and gases. Our model contains a large, low resistivity zone (C3) below the northern half of the Krafla volcanic field that domes upward to a depth of about 1.6 km b.s.l. C3 is partially coincident with reported low S-wave velocity zones which could be due to partial melt or aqueous fluids. The low resistivity could also be attributed to dehydration and decomposition of chlorite and epidote that occurs above 500 °C. As opposed to previously published resistivity models, our resistivity model shows that IDDP-1 encountered rhyolite magma near the upper edge of C3, where it intersects C2. In order to assess the sensitivity of the MT data to melt at the bottom of IDDP-1, we added hypothetical magma bodies with resistivities of 0.1 to 30 Ωm to our resistivity model and compared the synthetic MT data to the original inversion response. We used two methods to compare the MT data fit: (1) the change in r.m.s. misfit and (2) an asymptotic p-value obtained from the Kolmogorov–Smirnov (K–S) statistical test on the two sets of data residuals. We determined that the MT data can only detect sills that are unrealistically large (2.25 km3) with very low resistivities (0.1 or 0.3 Ωm). Smaller magma bodies (0.125 and 1 km3) were not detected; thus the MT data are not sensitive to small rhyolite magma bodies near the bottom of IDDP-1. Our tests gave similar results when evaluating the changes in r.m.s. misfit and the K–S test p-values, but the K–S test is a more objective method than appraising a relative change in r.m.s. misfit. Our resistivity model and resolution tests are consistent with the idea of rhyolite melt forming by re-melting of hydrothermally altered basalt on the edges of a deeper magma body.

Quench protection system for an HTS coil that uses Cu tape co-wound with an HTS tape

A quench protection system for a high-temperature superconducting (HTS) coil using Cu tape co-wound with an HTS tape was studied by numerical analysis using a thermal model of a coil winding pack. In normal operation, the voltage across the resistive zone Vs in the HTS coil was monitored by measuring the voltage difference between the HTS coil and the co-wound Cu coil. When Vs exceeded the quench detection voltage, the HTS coil was disconnected from the power supply and the energy stored in the HTS coil was dumped into a dump resistor. At the same time, the terminals of the co-wound coil were connected to another resistor, and some of the current in the HTS coil was quickly transferred to the co-wound Cu tape coil due to the tight magnetic coupling of both coils. This is expected to decrease the hot-spot temperature due to the quick decrease of HTS coil current and to protect the coil from damage caused by overheating at the hot-spot. The analysis investigated the effectiveness of this method.

A regional Alpine graphite décollement level beneath the NW Pannonian Basin

The so-called Transdanubian Conductivity Anomaly (TCA) of the Hungarian part of the NW Pannonian Basin has been well known for more than five decades. The exceptionally low resistivity (i.e. 1–2 Ωm) zone has a very large areal extent (on the order a few thousand km2) and it is an entirely subsurface anomaly occurring at depth between circa 3–15 km, with no corresponding outcrops. Various geological explanations of this enigmatic crustal-scale geophysical anomaly range from invoking sub-horizontal Alpine nappe contacts to sub-vertical dikes with graphite and/or saline fluid content. Only one possible analogue outcrop area was considered for the high conductivity anomaly so far, namely the Drauzug/Gailtal area of the Eastern Alps in Austria, some 300 km to the West from the TCA area. Previous attempts to find correspondence between the TCA and prominent seismic reflectors seen on 2D seismic reflection profiles were based on data acquired by research institutions. This study systematically correlates, for the first time, the TCA with 2D industry seismic reflection data in the same area. Our new results show a very strong correlation between the subsurface extent and location of the TCA with various sub-horizontally oriented Cretaceous Alpine nappe surfaces. In addition, we draw on the latest structural correlation of the Alpine nappe stack of the Transdanubian Range with its proper tectonic counterpart in the Eastern Alps.At the southern edge of the Upper Austroalpine units in northern Styria, in the Veitsch Nappe of the Greywacke Zone, numerous graphite localities are known historically. These laterally extensive graphite units in NW Styria formed as the result of greenschist-grade metamorphism of a Carboniferous coal sequence during the Cretaceous. For the first time, we describe here one well penetration of possibly age-equivalent graphitic units in NW Hungary. Correlation of the magnetotelluric anomaly with the distinct reflection seismic signature suggests that the same Palaeozoic graphitebearing Upper Austroalpine units should be present at 3–15 km depth in our study area.Therefore we propose that the best explanation for the observed extent and geometry of the TCA is the presence of graphite in subhorizontal, tectonically thinned detachment surfaces at the base of the Upper Austroalpine nappe edifice of NW Hungary

Noise Reduction for Transient Electromagnetic with High Cultural Noise: Case Study in Cisarua, Bandung Barat Regency

Transient Electromagnetic data acquisition was conducted in Cisarua, Bandung Barat Regency. Data are acquired using grounded dipole transmitter 500 meter spaced, with 13 A of current injected. TEM period are 40 s with 102 measurement period in total. Magnetic impedance sensor as receiver measured vertical magnetic field, located 400 meter from transmitter center point. The measurement area was located in a residential area and very close to man-made electromagnetic noise sources including power lines, radio and cellular transmitters. Periodic noise recorded along with transient signal was very strong, where the amplitude of 50 Hz noise is higher than the transient signal even at early time. This poses a challenge where a technique that capable of reducing noise and reconstructing the transient data are needed, so the data can further be processed in inversion program to create subsurface model. First technique used was statistical selection which is simple but proven effective in reducing noise in this condition without distorting the data. Data processing then continued by applying digital notch filter. After the transient signal are obtained, smoothness constrained least-square inversion are used to get the subsurface resistivity model, which shows 2 low resistivity zone. The shallower zone was supported by Electrical Resistivity Tomography data, and interpreted as shallow unconfined aquifer. The deeper zone was taught to be old volcanic products saturated with water associated with fault in the eastern area.

Application of TEM sounding method on riverbank filtration site subsurface suitability

Abstract Transient electromagnetic (TEM) sounding technology is known for its capability in detecting resistive zones, especially those associated with fresh water. Nevertheless, to date, there have been no available studies that have employed TEM for riverbank filtration (RBF) application. Therefore, this study was conducted to investigate the capability of TEM technology in profiling the subsurface of RBF areas adjacent to Sungai Perak, Kota Lama Kiri, Kuala Kangsar. A total of 27 survey points of simple rectangular loop configuration with loop area of 100 m2 (10 m × 10 m) were executed in the study area. A suite of TerraTEM equipment was used for the data acquisition process. The inversion and interpretation processes were then conducted by using the modeling program of ‘TDEM Geomodel’ and Surfer 13. The results showed four 2-D resistivity cross-section (depth–distance) profiles with their corresponding geological units. The interpretation results indicated that the subsurfaces of the study area were identified as alluvial-type soils (with a range of 10 to 40 Ωm) up to 8 m due to the presence of silt, sand and gravel. Based on the good quality results produced as well as its convenience, it is recommended that the TEM method is used for RBF exploration in future work.