Two-dimensional Resistivity Tomography Research Articles

Detection of Haqlaniyah cave within carbonate stratigraphic sequence rocks using 2D resistivity imaging technique, Haditha, western Iraq

The western desert of Iraq is characterized by a widespread karst phenomenon and caves. The study area is a site for the establishment of a primary school inAl- Haqlanighah village Haditha area, during leveling the land with a bulldozer, the ground collapsed, causing a hole with a diameter of up to two meters. Two-dimensional resistivity imaging has been applied to detect the depth and extent of the subsurface cave within carbonate rocks and along two cross-image lines in the array of Dipole-dipole and an electrode distance of 5 meters, each length of 105m. 2D Dipole-dipole imaging technique is obtained the inverse models which shows the resistivity variation between the anomalous of background resistivity of rocks and part of cavity is about 750:100 Ω.m. These models showed that the depth 11m at the cavity operator to the roof of cavity. While the actual depth at same location of this cavity measured of 11.35m approximately. The results of this study showed that the extension of the cave along the first track is 52 meters in a direction of west-east, 11 meters depth to the ceiling of the cave, 31-35 meters to the bottom of the cave. While the extension of this cave along the second track is 20 meters in a direction south-north, and the depth to the ceiling of the cave is 12 meters and 32-34 meters to the bottom of the cave. The stratigraphic succession of the study area, starting from bottom withAnah Formation, overlain by unconformity brecciated bed, ranging from 6 to 30m meters in thickness, followed by Euphrates Formation in the top. The unconformity layer is less cohesive than the rocks beneath and above it. So it was the best area for the caves to be formed as a result of dissolving its rocks by leaking rain water and groundwater. Therefore, it must be a pre-engineering preparation before starting any urban construction of the population in the study area or adjacent areas to avoid risks.

Using 2D Resistivity Imaging Technique to Detect and Delineate Shallow Unknown Cavities In Al-Haqlaniyah Area, Western Iraq

Basal breccia unconformity layer between Anah and Euphrates Formations in Al-Haqlaniyah area, Western desert, include enormous sinkholes and cavities usually cause severe damages to any kind of engineering facilities built over it. Two-dimensional resistivity imaging has been applied to detect the depth and extent of the subsurface caves at five stations. The dipole-dipole array is chosen with an electrode spacing of 2 meters. 2D Dipole-dipole imaging inverse models show the resistivity values have a big variation between the anomalous background resistivity of rocks and part of cavities. These models showed shallow cavities at 1 to 3 m depth and others at 5to 6 m depth and extending to a depth of 23 m. The unconformity layer is less cohesive than the rocks beneath and above it. So it was the best area for the caves to be formed as a result of dissolving its rocks by leaking rainwater and groundwater. Therefore, it must be a pre-engineering preparation before starting any urban construction of the population in the study area or adjacent areas to avoid risks.

Uncertainty of the 2D Resistivity Survey on the Subsurface Cavities

We examined the uncertainty of the two-dimensional (2D) resistivity method using conceptual cavity models. The experimental cavity study was conducted to validate numerical model results. Spatial resolution and sensitivity to resistivity perturbations were also assessed using checkerboard tests. Conceptual models were simulated to generate synthetic resistivity data for dipole-dipole (DD), pole-dipole (PD), Wenner–Schlumberger (WS), and pole-pole (PP) arrays. The synthetically measured resistivity data were inverted to obtain the geoelectric models. The highest anomaly effect (1.46) and variance (24,400 Ω·m) in resistivity data were recovered by the DD array, whereas the PP array obtained the lowest anomaly effect (0.60) and variance (2401 Ω·m) for the shallowest target cavity set at 2.2 m depth. The anomaly effect and variance showed direct dependency on the quality of the inverted models. The DD array provided the highest model resolution that shows relatively distinct anomaly geometries. In contrast, the PD and WS arrays recovered good resolutions, but it is challenging to determine the correct anomaly geometries with them. The PP array reproduced the lowest resolution with less precise anomaly geometries. Moreover, all the tested arrays showed high sensitivity to the resistivity contrasts at shallow depth. The DD and WS arrays displayed the higher sensitivity to the resistivity perturbations compared to the PD and PP arrays. The inverted models showed a reduction in sensitivity, model resolution, and accuracy at deeper depths, creating ambiguity in resistivity model interpretations. Despite these uncertainties, our modeling specified that two-dimensional resistivity imaging is a potential technique to study subsurface cavities. We inferred that the DD array is the most appropriate for cavity surveys. The PD and WS arrays are adequate, while the PP array is the least suitable for cavity studies.

Investigation of the Effect of Highway Runoff along Lagos-Badagry Expressway Using Electrical Resistivity Tomography and Physiochemical Methods

Geophysical and physiochemical investigations were carried out along Lagos-Badagry Expressway, Southwest, Nigeria on three locations dominated by highway runoff, with a view to monitoring the effect of highway runoff on nearby groundwater. The locations were: Iyana Isashi, Iyana Era and Agbara. An overview of the subsurface resistivity distribution was achieved employing Vertical Electrical Sounding (VES) using Schlumberger array and Two-dimensional (2D) resistivity imaging (Wenner array). The ABEM Terrameter SAS 1000 was used for both VES and 2D resistivity surveys and the data were analysed using IPI2win and RES2DINV, respectively. The VES results showed up to four geoelectric layers consisting of sand, clayey sand, clay and sandy soils. The resistivity at Agbara was found varying from 3.52 Ωm - 11 Ωm. This low resistivity value showed a high level of infiltration of highway runoff into the subsurface, thereby causing contamination of the groundwater. Iyana Isashi and Iyana Era have a relatively moderate resistivity values ranging from 103 Ωm to 178 Ωm. Physiochemical analysis of groundwater samples collected at the study locations revealed high electrical conductivity, total dissolved solids and pH values. The results of the borehole sample taken at 32 m away from the profile point at Agbara produced higher values of electrical conductivity and total dissolved solids than those of other locations, hence validating the electrical resistivity surveys, indicating that the groundwater sample from the survey point at Agbara is contaminated.

Impact of the geological structures on the groundwater potential using geophysical techniques in West Bani Mazar area, El Minia – Western Desert, Egypt

Establishment of the new agricultural projects in west Bani Mazar area, El Minia, Egypt needs a good knowledge about groundwater. Groundwater serves as the unique source of water supplies in the study area. Vertical Electrical Sounding technique is a convenient tool for groundwater exploration. This technique was utilized to illustrate the geoelectric succession, vertical and spatial extensions of the encountered layers, depth to water bearing layers and the structures affecting these layers. Profiling technique was carried out along a grid pattern using different half current electrode spacings (150 m, 300 m and 500 m) to clarify changes in resistivity values throughout the study area at different depths. Geoelectric layers B1 and B2 of the saturated zone are suitable for groundwater extraction in the study area. The resistivity values of the geoelectric layer B1 decrease towards the West direction, they decrease from 23.0 Ωm to 16.0 Ωm; and its thicknesses increase towards the SE direction from 12.0 m to 18.0 m. Whereas, the resistivity values of the geoelectric layer B2 decrease towards the NW direction from 40.0 Ωm to 26.5 Ωm; and its thicknesses vary from 34.0 m to 40.0 m. The depths to the upper surface of the water bearing layer B1 increase towards the NW direction from 44.0 m to 89.4 m. Based on the results obtained from the Vertical Electrical Soundings, four two-dimensional resistivity imaging profiles were measured at the selected sites. These 2-D resistivity profiles aim to determine depths to the water bearing layers, their thicknesses and the shallow structure. The inverted models of these profiles matched with the geoelectric sequence at these sites. In addition, a normal fault is detected at the northwestern part of the study area.According to the results obtained from this study it is clear that the groundwater in the area under consideration is occurred in the fractured limestone layers that belong to Eocene Age. Resistivity values of the water bearing layers increase with depth as a result of decreasing fracture density; and these values decreased towards the northwestern direction due to their proximity from the fault zone. The groundwater potential of these layers depends mainly on the lithologic composition and the geological structures affecting these layers. The secondary porosity of these limestone layers depends mainly on the degree of fracturing and fissuring. The proper sites to drill new productive wells were recommended, and the obtained data from drilling new well in the southeastern part of the study area coincide with the interpreted data of the different geophysical techniques.

River–groundwater connectivity in a karst system, Wellington, New South Wales, Australia

The characterization of river–aquifer connectivity in karst environments is difficult due to the presence of conduits and caves. This work demonstrates how geophysical imaging combined with hydrogeological data can improve the conceptualization of surface-water and groundwater interactions in karst terrains. The objective of this study is to understand the association between the Bell River and karst-alluvial aquifer at Wellington, Australia. River and groundwater levels were continuously monitored, and electrical resistivity imaging and water quality surveys conducted. Two-dimensional resistivity imaging mapped the transition between the alluvium and karst. This is important for highlighting the proximity of the saturated alluvial sediments to the water-filled caves and conduits. In the unsaturated zone the resistivity imaging differentiated between air- and sediment-filled karst features, and in the saturated zone it mapped the location of possible water- and sediment-filled caves. Groundwater levels are dynamic and respond quickly to changes in the river stage, implying that there is a strong hydraulic connection, and that the river is losing and recharging the adjacent aquifer. Groundwater extractions (1,370 ML, megalitres, annually) from the alluvial aquifer can cause the groundwater level to fall by as much as 1.5 m in a year. However, when the Bell River flows after significant rainfall in the upper catchment, river-leakage rapidly recharges the alluvial and karst aquifers. This work demonstrates that in complex hydrogeological settings, the combined use of geophysical imaging, hydrograph analysis and geochemical measurements provide insights on the local karst hydrology and groundwater processes, which will enable better water-resource and karst management.

Flow direction and velocity determination of dumpsite-induced groundwater contamination in part of Delta State, Nigeria

Contaminant flow direction and velocity from dumpsite in Osubi, Okpe area of Delta State, Nigeria, have been determined. Two-dimensional resistivity imaging, employing the dipole–dipole electrical resistivity technique, and radial resistivity sounding were used for this study. Also, the Groundwater Vistas version 4 was also used for particle/contaminant tracking, to determine flow direction and velocity. The low resistivity of 52 to 130 Ω-m of the topsoil and the second layer to a depth of about 25 m may be an indication of the presence of leachate from the dumpsite. The flow direction across the study area is in the NE–SW direction, which is in agreement with the flow direction generated from the anisotropy polar diagrams from the radial sounding. The path contour lines show the model groundwater steady state head distribution of the hydrogeological system of the area. An approximate head gradient of about 0.0006 towards the south-west was then calculated using the model output head distributions for the area. Therefore, from the groundwater flow equation, the flow velocity was calculated using the head gradient, porosity and hydraulic conductivity to be 0.0169 m/day or 6.0 m/year. If advective flow is assumed, therefore the contaminant would flow at an average speed of 0.0178 m/day or 6.0 m/year.

Resistivity imaging survey to delineate subsurface seepage of hydrocarbon contaminated water at Karbala Governorate, Iraq

This research is an attempt to accomplish a 3-D resistivity imaging survey, which was carried out near a water well contaminated with hydrocarbon materials in Karbala governorate. Two-dimensional resistivity imaging measurements were collected along four parallel profiles, using a Wenner array with electrode spacing of 1 m. The RES3DINV program was used to invert the apparent resistivity data. The results displayed a resistivity distribution of the subsurface in a three-dimensional volume. Thus, both the horizontal and vertical extents of the contaminated zone were displayed. This technique revealed a low resistivity zone at depth ranges from 3 to 6 m in the investigation area, but the seepage starts at depth ranges between 2 and 3 m and continues down depth (may be to the groundwater level). This low resistivity zone is the most likely location for a subsurface seepage of contaminated water. It is clear that the sufficient measurement points along 2-D lines in a small area can increase the 3-D imaging resolution, and nearly real 3-D imaging can be achieved, when the size of subsurface anomaly compared with the electrode spacing (a) of the Wenner array is taken into consideration.

Modeling of groundwater recharge using a multiple linear regression (MLR) recharge model developed from geophysical parameters: a case of groundwater resources management

In this paper we developed a simple multiple linear regression (MLR) recharge model that relates the recharge estimates obtained from rainfall to the geophysical parameters obtained from the interpretation of two-dimensional (2D) resistivity imaging data for the purpose of efficient groundwater resources management in the southern part of Perak, Malaysia through recharge rate estimation and prediction. Through application of linear regression model, the estimated recharge from rainfall and the corresponding estimated unsaturated layer resistivity and its thickness (Depth to aquifer top) parameters obtained from geophysical measurements were regressed in R software written code environment for generating a MLR recharge model. The sensitivity of analyzed results of the MLR recharge model based on the parameter estimation of the model predictors (resistivity and depth) evaluated at Pr ≤ 0.05 is 5.39 × 10−06 and 8.39 × 10−04, respectively. The accuracy and predictive power test conducted on the developed model using both t test and $$ \chi^{2} $$ distribution at α = 5 % significance level established the model estimation and prediction capability. The obtained results of $$ \chi^{2} $$ distribution test and parameters estimation test confirmed the reliability and accuracy of the proposed model in recharge rate estimation and prediction in the area. The application of the MLR recharge model gives estimate of 242.30 mm/year for regional groundwater recharge rate in the area. Through GIS tool, the MLR recharge model was used to produce groundwater recharge rate prediction map. A quick and independent estimate of recharge by simple geophysical measurement has been established based on these results. The information on the prediction map could serve as a scientific basis for groundwater resources management and exploration in the area. The approach suggests a new application of geoelectric parameters in determining recharge rate due to infiltration. The technique provides a good alternative to other methods used for this purpose.

Hydrogeophysical investigation and estimation of groundwater potentials of the Lower Palaeozoic to Precambrian crystalline basement rocks in Keffi area, north-central Nigeria, using resistivity methods

The use of resistivity sounding and two-dimensional (2-D) resistivity imaging was investigated with the aim of delineating and estimating the groundwater potential in Keffi area. Rock types identified are mainly gneisses and granites. Twenty-five resistivity soundings employing the Schlumberger electrode array were conducted across the area. Resistivity sounding data obtained were interpreted using partial curve matching approach and 1-D inversion algorithm, RESIST version 1.0. The 2-D resistivity imaging was also carried out along two traverses using dipole–dipole array, and the data obtained were subjected to finite element method modeling using DIPRO inversion algorithm to produce a two-dimensional subsurface geological model. Interpretation of results showed three to four geoelectrical layers. Layer thickness values were generally less than 2 m for collapsed zone, and ranged from 5 to 30 m for weathered bedrock (saprolite). Two major aquifer units, namely weathered bedrock (saprolite) aquifer and fractured bedrock (saprock) aquifer, have been delineated with the latter usually occurring beneath the former in most areas. Aquifer potentials in the area were estimated using simple schemes that involved the use of three geoelectrical parameters, namely: depth to fresh bedrock, weathered bedrock (saprolite) resistivity and fractured bedrock (saprock) resistivity. The assessment delineated the area into prospective high, medium and low groundwater potential zones.

Two-dimensional resistivity imaging in the Kestelek boron area by VLF and DC resistivity methods

Abstract A VLF and DC resistivity investigation was conducted in the Kestelek area, western Turkey, to determine the two-dimensional images of the boron deposits. The two-dimensional resistivity images were obtained by the inversion of tipper and resistivity data for VLF and DC resistivity methods, respectively. The VLF tipper data also were improved applying the Fraser and Karous & Hjelt (K&H) filtering to delineate the boundaries of the subsurface boron deposits. The main findings are: (1) moderate (> 25 Ωm) and relatively high (> 40 Ωm) resistivity zones in the two-dimensional models, which is mostly supported by the K&H real part of tipper as the negative current density peaks, may be interpreted as middle level of potatoes type colemanite and lower level of crystal type colemanite boron deposits inside the conductive units, respectively. (2) Transition from positive peaks (conductive zones) to negative peaks (resistive zones) in the K&H real part of tipper current density pseudosections may indicate the potential locations of the boron deposits. (3) Drilling well results obtained around two profiles of the study area are consistent with distribution of the resistive boron deposits in the two-dimensional resistivity models and K&H real part of tipper filtering images.

Two-dimensional resistivity imaging in the Kızıldere geothermal field by MT and DC methods

Magnetotelluric (MT) and Schlumberger (DC) surveys were conducted to identify conductive zones inside metamorphic complex in the easternmost part of B. Menderes Graben. In this study, using these surveying data, creation of some two-dimensional images of the shallow and deeper parts of the area was aimed. Broadband (200–0.002 Hz) MT and Schlumberger data were acquired along four profiles crossing the B. Menderes Graben with a total of 18 MT and 19 DC stations. These data were modeled using two-dimensional inverse techniques. The main findings are: (1) presence of wide conductive regions with very low resistivity (< 3 Ω m) are imaged at depth of ~ 100 m, extending to maximum ~ 2000 m depth, and these conductive regions signify potential geothermal resource in the area, (2) presence of deep conductive regions (< 75 Ω m) at a depth from ~ 15 km to 35 km, which reflects the shallow asthenosphere, could be correlated with the presence of high enthalpy geothermal system and its heat source.

Two‐dimensional resistivity imaging: a tool in archaeoseismology. An example from ancient Sagalassos (Southwest Turkey)

AbstractThe ancient Pisidian town of Sagalassos (southwest Turkey) was struck by several earthquakes during Roman and early Byzantine times and was abandoned around the middle of the seventh centuryAD, partly as the result of a devastating earthquake. A nearby epicentre is postulated, although the causative fault has not yet been identified. The identification of such an active fault is, however, important with respect to the assessment of the seismic hazard of the area. Two‐dimensional resistivity imaging has been used to detect the presence of an active normal fault passing underneath Sagalassos, as evidenced by geological, geomorphological and archaeoseismological observations. The resistivity profiles reveal the presence of five stratigraphical layers, i.e. from bottom to top: the bedrock composed of either limestone or ophiolitic me lange, the weathered top of this bedrock, old colluvial material, recent colluvial material that covers archaeological structures and recent scree deposits. The presence of active normal faults is, moreover, indicated by the displacement of the bedrock and the colluvial material on top of it. Offsets of archaeological structures at Sagalassos are likely to be the result of historical reactivations of these faults. The limestone front, overlooking Sagalassos from the north, probably corresponds to the degraded fault plane of the detected fault zone. Sagalassos was thus built on the hanging wall of an active normal fault. Two‐dimensional resistivity imaging proved to be an efficient tool in archaeoseismology. Copyright © 2003 John Wiley &amp; Sons, Ltd.

Evaluation of resistivity and seismic methods for hydrogeological mapping in karst terrains

A water exploration in a karst area can be hardly imagined without the application of electrical and seismic methods, but karst areas are very difficult environments for any geophysical exploration due to very high surface nonhomogeneities. Dual gradient mapping (measurements performed at two depth levels), two-dimensional (2-D) resistivity imaging, refraction methods and high-resolution reflection methods have been applied on a characteristic karst case in Croatia. General overview on the subsurface resistivity distribution has been reached by using the gradient mapping measurements. This revealed low-resistivity zone points of the fractured rock filled with water. Map of relative changes of apparent resistivities with depth discovers two different zones: resistivity increases with depth in the eastern part and resistivity decreases with depth in the western part of the area. Weak reflections are seen in the stacked seismic reflection section placed with the 2-D resistivity imaging profile, but they can be followed along the entire profile. By combining refraction and reflection data, faulted and fractured zones can be determined at surface as well as at greater depths, which will enable a precise definition of their extensions. Two-dimensional inverse seismic modelling have been carried out to clarify significance of the main reflection horizon, which is probably caused by a lithologic boundary, meaning a contact of dolomites and compact limestones. The model of acoustic impedancies has been derived on the basis of refraction velocities, reflection velocities and geological data from borehole. An accurate geological model has been established on the basis of all the data. Two-dimensional resistivity surveying can be used very efficiently in karst water explorations of shallow targets, but for deeper targets the seismic methods can be very useful by reason of poor resolution of the electrical resistivity methods.

The application of mise-á-la-masse and resistivity surveys to the detection of pollution from leaking sewers

Leakage of sewage from underground sewerage pipes can pollute waterways, and is of environmental and community concern. Traditional methods of analysis using flow gauging within the pipes, water quality monitoring within the receiving waters, and visual inspection within the pipes using closed circuit television are inadequate to precisely locate the source of the exfiltration.Tests were carried out to determine the effectiveness of the mise-á-la-masse method and two-dimensional resistivity imaging for locating the source of sewage leaks within sand- and clay-rich soils. The mise-á-la-masse method detects electrical continuity between the sewage and soil surrounding the pipe. An increase in electrical continuity, or a decrease in resistance, is caused by sewage leaking from within the electrically resistive sewerage pipes into the surrounding soils. Resistivity imaging measures the electrical resistivity in the subsurface as a function of depth below, and distance along the traverse. A decrease in resistivity, particularly at the depth of the sewerage pipe may be associated with the leakage of effluent.The mise-a-la-masse method is able to detect the leakage of pollution given a sufficient conductivity contrast compared with variations in the subsurface geological conditions. The resistivity pseudosections provide confirmation of the existence of a leak as a resistivity contrast in the vicinity of the pipe. The use of parallel traverses with the mise-á-la-masse method helps separate laterally continuous anomalies indicative of exfiltration from localised inhomogeneities.Tests at four sites in the Sydney area showed that electrical anomalies correlated with defects seen on within-pipe closed circuit television, and surface features, such as more prolific vegetation. This evidence strongly suggests leakage from the pipes, and indicates that surface geophysical methods are a viable method for detecting exfiltration.

Electrical resistivity imaging systems for ground investigations, with particular reference to dissolution features in Chalk areas

Abstract The collection of high-quality resistivity data using conventional systems is time-consuming, particularly where large areas are to be surveyed at small electrode spacings. With the advent of modern computer controlled resistivity meters, used in conjunction with multicore takeout cables and switched electrode arrays, two-dimensional resistivity imaging systems have been developed. These systems lend themselves to the search for small-scale, near-surface, anomalies due to their improved accuracy and resolution over more conventional equipment and their ability to produce true resistivity modelled images. Near surface dissolution features in the Chalk can produce variations in ground resistivity and this paper discusses the field trials of two resistivity imaging systems at the known locations of such features. The results are compared to those obtained using conventional resistivity equipment and related to ground truth data obtained by drilling.

Two-dimensional resistivity imaging and modelling in areas of complex geology : Griffith, D H; Barker, R D J Appl GeophysV29, N3/4, April 1993, P211–226

Two-dimensional resistivity imaging and modelling in areas of complex geology : Griffith, D H; Barker, R D J Appl GeophysV29, N3/4, April 1993, P211–226

Two-dimensional resistivity imaging and modelling in areas of complex geology

A system is described for the automatic measurement of electrical resistivity pseudo-sections. This comprises a linear array of up to 32 electrodes connected through a multicore cable to a computer controlled switching module and a resistivity meter. The processing of the measured sections to produce two-dimensional true resistivity images of the subsurface is briefly described. Some account is given of the capabilities and limitations of the technique. This is illustrated by a series of computed constant separation traverses for models of simple subsurface structures. Examples of processed images derived from sections measured in areas of relatively complex geology follow, a comparison being made of the interpretations obtained using an automatic imaging method and a manual iterative approach. It is concluded that with the equipment and software so far developed, in areas of modest subsurface geological complexity where some control is available and where the structures are essentially two-dimensional, then good approximations to the true geoelectric sections can be obtained down to depths of between 100 and 200 m.