ELECTRICAL RESISTIVITY TOMOGRAPHY

In this study, an integrated suite of geological and direct current resistivity (DCR) data is used to evaluate the hydrogeophysical conditions at the downstream part of Wadi Ramleiya, Eastern Desert, Egypt. Geological and morphometric analysis of drainage basin and DCR measurements in the form of 1D and 2D surveys are carried out to reveal the subsurface layer distributions and demonstrate the groundwater potentialities. It is obviously that the shallow aquifers and groundwater flow direction are related to structural controls. Based on the inversion results of DCR data, the aquifer is under unconfined conditions where it rests on layers of argillaceous limestone and overlain by gravelly sand. Accordingly, the obtained results can serve as a basis for monitoring, planning and management of water resources in such desert area, and as a whole, they constitute an encouraging example using an integrated approach of geological, morphometric and DCR data in groundwater exploration and fla...

Cross-borehole geoelectrical imaging, in particular electrical resistivity tomography (ERT) and transmission radar tomography, can provide high-resolution images of hydrogeological structures and, in some cases, detailed assessment of dynamic processes in the subsurface environment. Through appropriate petrophysical relationships, these tools offer data suitable for parameterising and constraining models of groundwater flow. This is demonstrated using cross-borehole radar and resistivity measurements collected during a controlled vadose zone tracer test, performed at a field site in the UK Sherwood Sandstone. Both methods show clearly the vertical migration of the tracer over a 200 h monitoring period. By comparing first and second spatial moments of changes in moisture content predicted from a numerical simulation of vadose zone flow with equivalent statistics from two-and three-dimensional ERT and cross-borehole radar profiles the effective hydraulic conductivity is estimated to be approximately 0.4 m/d. Such a value is comparable to field estimates from borehole hydraulic tests carried out in the saturated zone at the field site and provides valuable information that may be utilised to parameterise pollutant transport models of the site. q

The flood plain of the Nile River has been a safe dwelling throughout history. Recently with a growing population and vast growing urbanization some buildings have started to experience structural damages, which are not related to their construction design, but rather to the ground conditions around the buildings' foundations. Variations in properties of the soil supporting the buildings' foundations such as soil bearing capacity, moisture content and scouring may eventually lead to the failure of these buildings. This study is attempting to characterize the variations in the soil properties around the City Star shopping mall, in eastern Cairo, where a large building has tilted over the past few years. This tilting may lead to the collapse of the whole building if it continues at the same rate. An integrated geophysical investigation including multi-channel analysis of surface wave (MASW), ground penetrating radar (GPR) and 2-D electrical resistivity tomography (ERT) was used around the affected building to help detect possible causes of deterioration. The GPR data showed a soil-fill layer overlaying a thick bottom layer of higher moisture content. The MASW data revealed a middle layer of relatively low shear wave velocity sandwiched between two relatively high shear wave velocity layers. The ERT data showed an upper low resistivity layer overlying a high resistivity layer. Integrating the interpretations of the three geophysical methods provide a combined model that reflects lateral and vertical variation in the soil properties. This variation becomes dramatic near the tilted corner of the building.

Electrical resistivity tomography was used in order to explore an experimental site of the LaSalle Beauvais Polytechnic Institute (France). The test was conducted along a profile line of 315 m length, using 64 electrodes deployed at an interelectrode spacing of 5 m, and the data were recorded using gradient, Wenner and pole-dipole arrays. The performance of plate electrodes (non-conventional flat-based) is compared with the performance of peak electrodes (conventional spike). The hydrogeophysical investigation of the chalk aquifer system of Beauvais shows that the performance of plate electrodes is satisfactory, leading to inversions of small root-mean-square errors. Peak and the plate electrodes were tested before and after injection of a salt tracer in the piezometer of the experimental site. The study demonstrates the usefulness of plate electrodes (efficient, less time consuming) and the possibility of aquifer characterization by a salt tracer.

Resistivity method is developed rapidly during the 25 years ago. The most important method is 2D and 3D resistivity imaging, which is used for engineering, environmental, mining, etc. however, the vital feature that use to interpret 2D resistivity imaging is forward and inversion method, forward modeling is used to calculate what should be observed for practical model. It is an integral part for any inverse model. It is used finite element and finite difference methods to calculate the apparent resistivity for model produce by inversion method. Inversion method is a mathematical method of calculating cause from set of observation. This method used to determine the true resistivity of subsurface from apparent resistivity pseudosecton calculating in the field.it divided into three steps for each iteration. The first step is to calculate the apparent resistivity values for present model. This normally done by using finite-difference and finite-element. The second step is to calculate the Jacobian matrix of partial derivatives. Generally this step can be done by using Gauss-Newton or quasi-Newton methods. The third step is to solve the least-square equation where the Gauss-Newton or quasi-Newton methods are commonly used in least-square equation. Finally, bad data mainly effect the resolution and reliability of model and lead to wrong interpretation. Therefore, great attention must be paid to control the observed data quality in the field. If the data still have some noise, a damping factor and vertical and horizontal flatness filter the proper inversion parameters that control the inversion method. For noisy data, a large damping factor is used (eg. 0.3) and small damping for less noisy data (eg. 0.1). Vertical and horizontal flatness filter allows the user to fine-tune the smoothness constrain to emphasizes vertical and horizontal structure in the inversion method.

The detection and mapping of unmarked graves is a significant focus of many archaeological and forensic investigations
however traditional methods such as probing, forensic botany, cadaver dogs or dowsing are often ineffective, slow to cover large areas
or excessively invasive. Geophysics offers an appealing alternative suitable for the rapid non-invasive investigation of large areas.
Unfortunately graves are a challenging target with no diagnostic geophysical response and so the use of a rigorous application-specific
methodology is essential for a successful outcome. The most important inclusions in a successful survey methodology include ultrahigh density data, the use of multiple geophysical techniques to validate results based on several physical properties, excellent quality
positioning and intensive site recording. Regardless of the methodology applied, geophysics should not be considered a panacea for
locating all graves on all sites but should be used as an integral part of a comprehensive survey strategy

The flood plain of the Nile River has been a safe dwelling throughout history. Recently with a growing population and vast growing urbanization some buildings have started to experience structural damages, which are not related to their construction design, but rather to the ground conditions around the buildings' foundations. Variations in properties of the soil supporting the buildings' foundations such as soil bearing capacity, moisture content and scouring may eventually lead to the failure of these buildings. This study is attempting to characterize the variations in the soil properties around the City Star shopping mall, in eastern Cairo, where a large building has tilted over the past few years. This tilting may lead to the collapse of the whole building if it continues at the same rate. An integrated geophysical investigation including multi-channel analysis of surface wave (MASW), ground penetrating radar (GPR) and 2-D electrical resistivity tomography (ERT) was used around the affected building to help detect possible causes of deterioration. The GPR data showed a soil-fill layer overlaying a thick bottom layer of higher moisture content. The MASW data revealed a middle layer of relatively low shear wave velocity sandwiched between two relatively high shear wave velocity layers. The ERT data showed an upper low resistivity layer overlying a high resistivity layer. Integrating the interpretations of the three geophysical methods provide a combined model that reflects lateral and vertical variation in the soil properties. This variation becomes dramatic near the tilted corner of the building.

A segment of the Upper Rhine River presenting both anastomosed and braided was investigated. This area gives us the opportunity to study settlement dynamics during two key periods of the Holocene. The Roman Period characterised by a first major anthropogenic impact on the environment and poorly documented climatic changes. The Little Ice Age, when human settlement and climate may be well documented with high reliability.
A wide methodological approach has been completed to combine results from geomorphology, stratigraphy, geophysics, G.I.S., palynology, dendrochronology and archaeology. This dataset shows:
1/ documentary flood frequency variations of the Rhine River during the last 800 years. These chronological variations show some dissimilarity with other French rivers reconstructed documentary flood series. That attests a primary control of catchment’s characteristics and regime type on long term hydrological dynamics.
2/ changes in the Rhine River and floodplain dynamics during Little Ice Age before major anthropogenic river management of 19th century. Planform changes, riverine forest, land use evolution, and anthropological settlement processes are described and quantified. These results allow the identification of major stratigraphic agent factors role responsible of these changes.
3/ the alluvial landscape character where the Oedenburg site settled, together with the evolution of the riverine forest influenced by the Rhine River hydrodynamics.
4/ settlement dynamics during Antiquity. Four major settlement phases have been evidenced by spatial distribution analysis of roman coins found by pedestrian prospecting during the last twenty years. Settlement dynamics may have been influenced by either historical or environmental impacts.
5/ variations in alluvial dynamics of the Rhine River during Antiquity such as high water table or flooding events.

Ur, the city of the moon god and “Home of Abraham” was founded by settlers in the 4th millennium BC. The remains of the site are located 345km south of Baghdad and 257km away from the Persian Gulf. It is one of the most prominent cities in Mesopotamia (Wooley 1934-1976). There is evidence that the occupation was ended by a flood, formerly attributed to the flood described in Genesis. Although the city is much smaller than Uruk, in the next (Early Dynastic) period Ur became the capital of southern Mesopotamia under the Sumerian kings of the 1st dynasty of Ur (25th century BC). The last king, who left his traces both at Ur and Uruk was the Achaemenian Cyrus the Great, whose inscription on bricks was found in recent excavations.
The cities survived until the reign of Artaxerxes II. It was perhaps at this time that the Euphrates changed its course. With the breakdown of the whole irrigation system of Ur, its fields reduced to a desert and were finally abandoned.
For this research, we used 2D and 3D Electrical resistivity tomography (ERT) to unveil the underground structures of this city.

Geophysical surveys for cavity detection are one of the most common nearsurface applications. The usage of resistivity methods is also very straightforward for the air-filled underground voids, which should have theoretically infinite resistivity in the ERT image. In the first part of the paper, we deal with the comparison of detectability of the cavity by several types of the electrode arrays, the second part discusses the effect of a thin layer around the cavity itself, by means of 2D modelling. The presence of this layer deforms the resistivity image significantly as the resistive anomaly could be turned into a conductive one, in the case when the thin layer is more conductive than the background environment. From the electrical array analysis for the model situation a dipole-dipole and combined pole-dipole shows the best results among the other involved electrical arrays.

Set of parallel oriented ERT profiles was used for identification of fluvial channels in the area near the Western Gate of the Great Moravia Empire agglomeration Pohansko near Břeclav. Three infills of fluvial channels were identified within the ERT profiles, which erosively cut the complex of flood loams. The dimensions of these channels are compared, together with the distribution of individual architectural elements of the channel. Planform topography of individual channels is used for evaluation of fluvial style. Whereas Early Mediaval age of the sedimentary infill of the uppermost channel was proved, the two lower channels are supposed to be Upper Pleistocene to Early Holocene in age. The highly irregular relief of the Pannonian clays of the Vienna Basin forms the Pre-Quaternary basement.

— In the last two decades the village of Casalabate was affected by a number of sinkhole events, the last episode occurring on 7 January 2012. Due to some geological and geotechnical uncertainties, Casalabate became an intriguing case study of sinkhole hazard in urban areas and three geological-geophysical models were recently proposed by three different studies. In this paper new geophysical data and some epistemological consideration were done. The results are a contribution to an efficient predictive model that could be well define both the geological setting and sinkhole hazard. Keywords— urban environment, sinkhole geohazard, electrical resistivity tomography, ground penetrating radar, karst coastal plane; new data

The Causse of El Hajeb belongs to the Tabular Middle Atlas (TMA), in which thousands of karst landforms have been identified. Among them, collapse dolines and dissolution sinkholes have been highlighted as a source of environmental risks and geo-hazards. In particular, such sinkholes have been linked to the degradation of water quality in water springs located in the junction of the TMA and Saïss basin. Furthermore, the developments of collapse dolines in agricultural and inhabited areas enhance the risk of life loss, injury, and property damage. Here, the lack of research on newly formed cavities has exacerbated the situation. The limited studies using remote sensing or geophysical methods to determine the degree of karstification and vulnerability of this environment fail to provide the spatial extent and depth location of individual karst cavities. In order to contribute to the effort of sinkhole risk reduction in TMA, we employed remote sensing and geophysical surveys to integrate electrical resistivity tomography (ERT) and self-potential (SP) for subsurface characterization of four sinkholes identified in the Causse of El Hajeb. The results revealed the existence of sinkholes, both visible and non-accessible at the surface, in carbonate rocks. The sinkholes exhibited distinct morphologies, with depths reaching 35 m. Topography, geographic coordinates and land cover information extracted on remote sensing data demonstrated that these cavities were developed in depressions in which agricultural activities are regularly performed. The fusion of these methods benefits from remote sensing in geophysical surveys, particularly in acquisition, georeferencing, processing and interpretation of geophysical data. Furthermore, our proposed method allows identification of the protection perimeter required to minimize the risks posed by sinkholes.

The presence of natural voids and cavities in subsurface karstic limestones causes severe problem for civil engineering and environmental management. The presence of such features hinders the extension of urbanizations particularly in the new metropolitan. The eastern part of Saudi Arabia contains various types of karstic limestone, sinkholes, solution cavities and voids. In this context, geophysical methods particularly electrical resistivity technique is used as a cost-effective solution for investigating subsurface caves, voids, and shallow weathered zones. 2-D electrical resistivity data sets have been acquired along seven profiles in the new urbanization at Al Hassa area. Data processing has been carried out taking into consideration the response of synthetic models, which simulates physical models of the most common karstic features in the area. The results are very useful to determine the extension of shallow weathered zones and to locate different cavities underneath them. The hard limestone bedrock can also be detected and traced along the surveyed profiles.

Collapse dolines are closed karst depressions of various size and morphology, which can be found all over the Slovenian karst. A collapse of cave chamber roofs is the basic mechanism of their formation. Limited dimensions of cave chambers result only in the formation of small collapse dolines. The formation and allocation of collapse dolines of greater dimensions are closely related to specific underground hydrology in areas with concentrated underground water flow, water table oscillation and higher corrosion or erosion in cave passages. The analysis of collapse dolines morphology and the interpretation of processes lead to the understanding of dynamics and mechanisms of collapse dolines formation and transformation with various geomorphic processes. The dissertation introduces the new models of processes in collapse dolines, which can be used for the interpretation of collapse dolines development in time context or for interpretation of mechanics and dynamics of specific geomorphologic processes.

Information about the internal structure of rock glaciers is needed to understand their reaction to ongoing climate warming. Three different geophysical techniques-shallow seismic refraction, ground-penetrating radar (GPR) and electrical resistivity tomography-were used to develop a detailed subsurface model of the Green Lake 5 rock glacier in the Colorado Front Range, USA. Below a thin zone of fine sediments and soils (0.7 -1-m thickness; 0 -20 kVm and 320 -370 m s À1 ), a 1 -3-m thick zone with low p-wave velocities (790 -820 m s À1 ) and high electrical resistivity (20 -100 kVm) is interpreted as the ice-free, blocky active layer with large void spaces. The data corroborate strong reflections of the GPR signals which travel at this depth at 0.11 m ns À1 . A third layer that extends from depths of 1 -3 m to about 5 m is characterised by lower electric resistivities (5 -20 kVm) and has lower electromagnetic wave velocities (0.65 m ns À1 ), representing unfrozen, finer and wetter sediments. At around 5-m depth, the measured physical parameters change drastically (vp ¼ 3200 -3300 m s À1 , 50 -150 kVm, vGPR ¼ 0.15 m ns À1 ), showing an ice-rich permafrost zone above the bedrock. This model of the internal structure was used to evaluate an existing hydrological flowpath model based on the hydrochemical properties of water outflow from the rock glacier.

This work aims to investigate the applicability of electrical resistivity tomography (ERT) as a non-destructive tool of agricultural soil characterization after digestate of fruit and vegetable (DFV) amendment application. DFV was applied at 30 t ha −1 in one application (D1), split into 2 (D2) and 6 applications (D6), and compared with initial state (IS) on field plots of 10 m 2. The high-resolution 2D ERT prospecting was performed using a ABEM SAS4000 multi-electrode Lund imaging survey system with a set of 16 electrodes evenly spaced 0.1 m. The resistivity values with ERT profiles using the Wenner array range globally from 0 to 200 Ω m. All treatments proposed decreased soil resistivity to 0-30 cm depth profile. Splitting digestate shows more intensive decreasing resistivity in the top layer and less in the bottom, and moves the iso-resistivity lines lower than 30 Ω m from 7 cm depth to 12, 20, and 30 cm depth, respectively, for D6, D2, and D1. The resistivity folding at 15 to 30 cm depth was 87, 80, and 67% then 58, 42, and 37%, respectively, for D1, D2, and D6. The low resistivity values may be due to soil organic matter flow illustrated. Digestate applied once acted on the soil with heterogeneous way along the profile. Splitting it increases the thickness of foam layer homogeneously. ERT seems a promising technique for the survey of soil organic matter content monitoring, dispersion, and assessment.

The presence of natural voids and cavities in subsurface karstic limestones causes severe problem for civil engineering and environmental management. The presence of such features hinders the extension of urbanizations particularly in the new metropolitan. The eastern part of Saudi Arabia contains various types of karstic limestone, sinkholes, solution cavities and voids. In this context, geophysical methods particularly electrical resistivity technique is used as a cost-effective solution for investigating subsurface caves, voids, and shallow weathered zones. 2-D electrical resistivity data sets have been acquired along seven profiles in the new urbanization at Al Hassa area. Data processing has been carried out taking into consideration the response of synthetic models, which simulates physical models of the most common karstic features in the area. The results are very useful to determine the extension of shallow weathered zones and to locate different cavities underneath them. The hard limestone bedrock can also be detected and traced along the surveyed profiles.

Recent changes in the fluvial dynamics of the middle Garonne river (SW France) are approached by combining historical maps and data field (cores and Electrical Resistivity Tomographies – ERT). This study is carried out at the scale of a 5 km length reach in the Grenades-Ondes area, 22.5 km N-NW of Toulouse. The results retrace the changes of the system over a period of about one millennium. These results show a significant modification between: 1) a state of reduced hydro-dynamism during the central Middle-Age (XIth XIIIth centuries AD); 2) a revival in the fluvial dynamics during the modern period, related to the Little Ice Age (early XIXth century); and 3) a current trend to contraction and simplification of the channel, started from the mid-nineteenth century, probably as a result of combined effects of local human and hydro geomorphological factors and a decrease in major flood related to the end of the LIA.

A study of cerebral hemorrhage detection using computed tomography with head image has been done. The process after detection is the determination of the area and volume of hemorrhage. Image processing techniques used are Segmentation of Otsu method. This segmentation method successfully obtained binary image and proceed with morphology process, with output image result of morphology operaionis calculated the area. After the area of the object on each image slice is obtained, the next step is the volume calculation. Volume calculation is done by summing the area of the object on each slice then the result multiplied by the slice thickness. The result of the use of image processing techniques can be offered as a substitute for manual calculating by doctors. Keywords— Cerebral hemorrhage, segmentation of otsu method, computed tomography, area and volume.

The study of electrical resistivity anisotropy in rocks has become important in increasing the accuracy of geological mapping using electrical resistivity survey. The study area, Iwaro-Ayepe in Akoko, southwestern Nigeria, has been surveyed using electrical resistivity soundings in delineation and characterization of the subsurface fracture.
The geological survey showed that the area comprises of granite-gneiss, grey-gneiss and granite. A rose diagram was also produced from values obtained during the geological exercise.
The geophysical survey was carried out in five locations, azimuthal resistivity soundings (ARS) were carried out at each location making a total of twenty (ARS) points. The data obtained were then subjected to various forms of interpretations which includes; computer iterated curves, radial plots and graph of degree of fracture. The resistivity curves comprise of three layer curve types and this includes H, K, Q, and A curve types. The fracture system according to the geological survey (rose diagram) and the ARS, indicates the presence of a localized fracture system which shows mainly NE-SW, NW-SE, E-W trends and very good degree of fracture in location 2, 3, and 4 which is well spread throughout the electrode spacing.
The subsurface fracture characterization is well localized and has directional properties as shown by the geological and geophysical results.

The  phenomenon  of  building  collapse  in recent  times  has  become  a  source  of  national concern. Particularly alarming is the situation in Lagos,  the  commercial  nerve  center  of  Nigeria.
Several  attempts  made  to  proffer  solution  to this  excluded  geophysical  investigations,  as general  opinion  did  not  support  subsurface geology as being responsible. However, 2-D and
3-D  electrical  resistivity  surveys  were  carried out    using    wenner    electrode    configuration with  64  electrodes  connected  to  a  multi-core cable,  along  three  (3)  profiles  of  260  m  length at  an  inter-electrode  spacing  of  4m.  Resistivity
measurements were    taken    alongside    with Induced  Polarization  measurements  using  the same  electrode  configuration.  The  survey  was conducted  round  to  cover  all  the  areas  where distress in building structures is noticeable. The
2-D and 3-D electrical resistivity and IP images for  the  three  profiles  revealed  that  the  main cause  of  structural  defect  in  buildings  around the  area  is  the  subsurface  geology,  contrary  to general opinion which favours insufficiency and/or lack of genuine building materials. From the results,  it  is  quite  obvious  that  the  entire  land mass of the study area is underlain by materials of  very  low  resistivity  values  below  30  Ωm  at
the  near-surface  depth  of  5  m  down  to  above 30  m.  Local  high  resistivity  in  the  near  surface material  is  due  to  either  the  effect  of  sand-filling  for  road  network  and/or  the  presence  of exotic  highly  resistive  concrete  materials  used
to reclaim land. The IP inversion models help to delineate  clay  formation  from  sandy  formation filled  with  saline  water.  The  high  IP  signals  in the  subsurface  mainly  confirm  the  presence  of clayey formation.

Natural processes are known to cause significant damage to archaeological monuments. In fact, the key to understanding the decay of building materials is the internal movement of water through the mineral matrix, which influences the distribution of chemical, physical and biological deterioration processes. Electrical resistivity tomography (ERT) was traditionally used as a surveying tool within archaeology, but a new high-resolution technique that accurately traces the movement of moisture in building materials could provide a vital tool for understanding the decay of many archaeological monuments. This paper considers current progress, the shift of ERT from soil to rock research and the impact that this development could have on future conservation, using Hertford College (Oxford) and Neolithic rock art (Golden Gate Reserve, South Africa) as case studies.

Rapid growth of residential colonies around the campus of the CSIR-National Geophysical research Institute (NGRI), Hyderabad during the last two decades has resulted in either disappearance or drastic reduction in size of open space and ponds for groundwater recharging. Withdrawal of groundwater for domestic uses has increased several fold causing continuous lowering of the water table in and around the campus. Due to this changed scenario availability of groundwater to meet the requirement of CSIR-NGRI is drastically reduced. This communication presents the results of electrical resistivity tomography (ERT) carried out in the CSIR-NGRI premises to locate potential groundwater resources as well as choose suitable sites for artificial recharging of aquifer. Groundwater potential zone identified by ERT is verified at one site by drilling a bore well.

This paper deals with the resistivity continuous surveys on extensive area carried out at the Mont'e Prama archaeological site, in Sardinia (Italy). From 2013 to 2015, new research was performed using both non-destructive surveys and traditional archaeological excavations. The measurements were done in order to find geophysical anomalies related to unseen buried archaeological remains and to define the spatial extension of the ancient necropolis. The electrical resistivity of soils was measured by means of the Automated Resistivity Profiling (ARP©) system. This multi-pole method provided high-resolution maps of electrical resistivity in the whole investigated area using a computer-assisted acquisition tool, towed by a small vehicle. Through this acquisition layout, a surface of 22,800 m 2 was covered. The electrical resistivity data were derived in real time with centimetric horizontal precision through a differential GPS positioning system. Thanks to the simultaneous acquisition of ARP and GPS data, the rigorous georeferencing of the tridimensional experimental dataset was made possible, as well as the reconstruction of a detailed Digital Terrain Model. Here, the experimental results are analyzed and critically discussed by means of the integration of the results obtained by a high-resolution prospection performed with a multi-channel Ground Penetrating Radar system and taking into account other information derived from previous geological and archaeological studies. Geophysical results, jointly with topographic reconstruction, clearly permitted the identification of more interesting areas where future archaeological investigations could be focused.

The article shows the results of geophysical surveys performed by using Electrical Resistivity Tomography (ERT) method on selected region of Płock slope of a Tumski hill near Basilica of Assumption of the Blessed Virgin Mary in Płock and in Maszewo by the Vistula River a few kilometers north of Płock. The above-mentioned sections were selected due to landslide phenomena observed there. Geophysical surveys were conducted in order to verify the state of the distribution of electrical resistivity in the sectors where mass movement was identified. The electrofusion cross-section near Cathedral Basilica shows clays and sands. Also in ERT prospection a zone of loose soils with high resistance is clearly visible. The results of the ERT method from Maszewo, indicates historical land surface of a landslide and that the slope in Maszewo consists of cohesive deposits. In order to describe these particular issues, geological cross-sections and safety factor obtained by calculation are presented for the analyzed parts of the slope. The safety factor shows that probability of landslide activity near Cathedral Basilica is very unlikely and in Maszewo is very high

A geophysical study by means of electrical resistivity and induced polarization tomographies was carried out in the landfill site of Bellolampo (Palermo, Italy) to check the integrity of the landfill liner and to detect possible leachate plumes. Preliminarily, synthetic tests were performed, simulating acquisition data along profiles placed above resistivity distribution, suitable to represent landfills protected with an high-density polyethylene (HDPE) liner at the bottom or with possible leachate plumes. Optimized array data sets for parallel measurements have been tested in order to assess the resolution and the effectiveness of tomographic images, comparing inversions with and without the constraint of the HDPE liner position. Based on the obtained results, three electrical tomographies have been planned and carried out directly over the landfill and nearby. The results provided useful information for identifying the electrical properties of the rock, waste, and leachate; for identifying snags and disruption of the tank bottom liner; and for pointing out possible polluting leachate nearby and below the landfill.

Tidal dynamics and especially storm surges can have an extensive impact on coastal fresh groundwater resources. Combined with the prospect of sea-level rise and the reliance of many people on these resources, this demonstrates the need to assess the vulnerability of coastal areas to these threats. In this study, we investigated the impact of tides and storm surges on coastal groundwater at a pilot location on the Dutch coast (viz., the Sand Engine). To monitor changes in groundwater salinity under a variety of conditions, we performed automated measurements with electrical resistivity tomography for a period of 2 months between November 2014 and January 2015. The obtained resistivity images were converted to salinity images, and these images served effectively as observations of the impact of tidal fluctuations, saltwater overwash during storm surges, and the recovery of the freshwater lens after land-surface inundations. Most of the observed changes in groundwater head and salinity could be reproduced with a two-dimensional variable-density groundwater flow and salt transport model. This shows that groundwater models can be used to make accurate predictions of the impact of tides and storm surges on fresh groundwater resources, given a thorough understanding of the (local) system. Comparisons of measurements and model simulations also showed that morphological changes and wave run-up can have a strong impact on the extent of land-surface inundations in (low-elevation) dynamic coastal environments, and can therefore substantially affect coastal fresh groundwater resources. Plain Language Summary Most coastal regions in the world rely on groundwater as their main source of fresh water. The availability of fresh water in many coastal communities is threatened by population growth, sea-level rise, and increases in the number and intensity of storm surges. This threat raises the importance of an optimal management of fresh groundwater in coastal areas to limit the salinization of fresh groundwater resources. However, the management of coastal groundwater is often complex and data is limited. In this research we have successfully used electrical resistivity tomography to measure effect of tides and storm surges on fresh groundwater at a pilot location on the Dutch coast (called the Sand Engine). In addition, most of the measured changes in groundwater head and salinity could be imitated with a numerical groundwater model. This proved that with a thorough understanding of the local system, groundwater models can be used to make accurate predictions of the impact of tides and storm surges on fresh groundwater resources.

Electrical resistivity tomography was used in order to explore an experimental site of the LaSalle Beauvais Polytechnic Institute (France). The test was conducted along a profile line of 315 m length, using 64 electrodes deployed at an interelectrode spacing of 5 m, and the data were recorded using gradient, Wenner and pole-dipole arrays. The performance of plate electrodes (non-conventional flat-based) is compared with the performance of peak electrodes (conventional spike). The hydrogeophysical investigation of the chalk aquifer system of Beauvais shows that the performance of plate electrodes is satisfactory, leading to inversions of small root-mean-square errors. Peak and the plate electrodes were tested before and after injection of a salt tracer in the piezometer of the experimental site. The study demonstrates the usefulness of plate electrodes (efficient, less time consuming) and the possibility of aquifer characterization by a salt tracer.

A large-scale electrical resistivity tomography (ERT) survey was undertaken around the Neolithic tell of Szeghalom-Kovácshalom in southeast Hungary, covering an area of almost 6 ha. High-resolution ERT data were collected along 28 uniformly distributed transects of variable length using the roll-along technique. A recently presented two-dimensional fast non-linear resistivity inversion algorithm was used to invert the ERT data and recover the true subsurface resistivity distribution along the specific cross-sections. The algorithm calculates and stores in an efficient manner the part of the Jacobian matrix that is actually important within the inversion procedure, thus rendering it almost 4.8 times faster than the algorithm that calculates the complete Jacobian matrix, without losing quality. The algorithm was further modified to account for any non-standard electrode configuration. A recently established iterative algorithm for sparse least squares problems (LSMR) was incorporated for the first time into the algorithm to solve the inverse resistivity problem. The effectiveness and robustness of the LSMR solver was highlighted through the processing of all the ERT lines. The processing and evaluation of the ERT data made it possible to map the thickness of the anthropogenic layer below the surface of the tell, to outline the horizontal and vertical dimensions of the palaeochannel adjacent to the tell, and to determine the general stratigraphy of geological layers up to 10 m below the ground surface. The ERT results also were used to update an older topographic map of the site showing the course of the palaeochannel around the tell. A synthetic model verified and enhanced the conclusions based on the field data. This study illustrates the added value that a systematic ERT survey can provide in reconstructing the ancient fluvial geomorphology of a microregion as well as the depth and horizontal extent of deposits associated with human habitation at archaeological sites. Figure 6. Surface maps showing the topographic relief of the different stratigraphic layers around the Szeghalom-Kovácshalom tell. (a) Thickness of the topsoil and anthropogenic Layer. (b) Thickness of the palaeochannel. (c) Thickness of the silty clay and silty clay with sand layer. (d) Burial depth of the deepest clayey layer. This figure is available in colour online at wileyonlinelibrary.com/journal/arp Figure 7. Overlay of the outline of the palaeochannel on an old topographic map of the tell. The solid and dashed lines indicate respectively the definite and prospective boundaries of the palaeochannel as extracted by the ERT survey. This figure is available in colour online at wileyonlinelibrary.com/journal/arp

A validation experiment, carried out in a scaled field setting, was attempted for the long electrode electrical resistivity tomography method in order to demonstrate the performance of the technique in imaging a simple buried target. The experiment was an approximately 1/17 scale mock-up of a region encompassing a buried nuclear waste tank on the Hanford site. The target of focus was constructed by manually forming a simulated plume within the vadose zone using a tank waste simulant. The long electrode results were compared to results from conventional point electrodes on the surface and buried within the survey domain. Using a pole-pole array, both point and long electrode imaging techniques identified the lateral extents of the pre-formed plume with reasonable fidelity but the long electrode method was handicapped in reconstructing vertical boundaries. The pole-dipole and dipole-dipole arrays were also tested with the long electrode method and were shown to have the least favourable target properties, including the position of the reconstructed plume relative to the known plume and the intensity of false positive targets. The poor performance of the pole-dipole and dipole-dipole arrays was attributed to an inexhaustive and non-optimal coverage of data at key electrodes, as well as an increased noise for electrode combinations with high geometric factors. However, when comparing the model resolution matrix among the different acquisition strategies, the pole-dipole and dipole-dipole arrays using long electrodes were shown to have significantly higher average and maximum values within the matrix than any pole-pole array. The model resolution describes how well the inversion model resolves the subsurface. Given the model resolution performance of the pole-dipole and dipole-dipole arrays, it may be worth investing in tools to understand the optimum subset of randomly distributed electrode pairs to produce maximum performance from the inversion model.

Occurrences of surficial karstic depressions in south-central Georgia are generally attributed to the dissolution within the Floridan aquifer even though it is overlain by a confining unit of varying thickness. This study explores the karst development within the carbonate layers of the confining unit using geophysical investigation techniques, namely electrical resistivity tomography (ERT), and ground penetrating radar (GPR). Surveys at sites of observed surficial depressions reveal shallow karst development which is unrelated to the deeper karst processes within the Floridan aquifer. The overlying unit, generally comprised of impermeable siliciclastic sediments, appears to have lower degrees of confinement at sites of increased karst development where carbonate layers are present. This has important implications not only for structural stability of the area, but also for the environmental sensitivity of the Floridan aquifer.

Investigating sinkhole morphology and formation mechanisms is key to understanding their long term impact and susceptibility to development, and aids in the design of effective mitigation measures. In this study, ERT (electrical resistivity tomography), MASW (multichannel analysis of surface waves) and borehole data were used to image the subsurface morphology of an active sinkhole in Greene County, Missouri. The study reveals that the sinkhole developed along a natural surface drainage pathway above a pervasively fractured limestone. The subsurface image of the sinkhole depicts a zone of near-vertical water seepage and soil piping. Based on the nature of the overburden material, and the morphology and current/past surface expression of the sinkhole, it is concluded that the sinkhole is predominantly a cover subsidence type of sinkhole. However, it is possible that minor cover collapse occurred locally and in an area slightly to the north of the current active sinkhole.

Electrical resistivity tomography is a well-known technique to monitor fresh-salt water transitions. In such environments, boreholes are often used to validate geophysical results but rarely used to constrain the geoelectrical inversion. To estimate the extent of salt water infiltration in the dune area of a Natural Reserve (Westhoek, Belgium), electrical resistivity tomography profiles were carried out together with borehole electromagnetic measurements. The latter were used to calculate a vertical variogram, representative of the study site. Then, a geostatistical constraint, in the form of an a priori model covariance matrix based on the variogram, was imposed as regularization to solve the electrical inverse problem. Inversion results enabled to determine the extension of the salt water plume laterally and at depth, but also to estimate the total dissolved solid content within the plume. These results are in agreement with the hydrogeological data of the site. A comparison with borehole data showed that the inversion results with geostatistical constraints are much more representative of the seawater body (in terms of total dissolved solids, extension and height) than results using standard smoothness-constrained inversion. The field results obtained for the Westhoek site emphasize the need to go beyond standard smoothness-constrained images and to use available borehole data as prior information to constrain the inversion.

This paper deals with the resistivity continuous surveys on extensive area carried out at the Mont’e Prama archaeological site, in Sardinia (Italy). From 2013 to 2015, new research was performed using both non-destructive surveys and traditional archaeological excavations. The measurements were done in order to find geophysical anomalies related to unseen buried archaeological remains and to define the spatial extension of the ancient necropolis. The electrical resistivity of soils was measured by means of the Automated Resistivity Profiling (ARP©) system. This multi-pole method provided high-resolution maps of electrical resistivity in the whole investigated area using a computer-assisted acquisition tool, towed by a small vehicle. Through this acquisition layout, a surface of 22,800 m2 was covered. The electrical resistivity data were derived in real time with centimetric horizontal precision through a differential GPS positioning system. Thanks to the simultaneous acquisition of ...

Rapid growth of residential colonies around the campus of the CSIR-National Geophysical research Institute (NGRI), Hyderabad during the last two decades has resulted in either disappearance or drastic reduction in size of open space and ponds for groundwater recharging. Withdrawal of groundwater for domestic uses has increased several fold causing continuous lowering of the water table in and around the campus. Due to this changed scenario, availability of groundwater to meet the requirement of CSIR-NGRI is drastically reduced. This communication presents the results of electrical resistivity tomography (ERT) carried out in the CSIR-NGRI premises to locate potential groundwater resources as well as choose suitable sites for artificial recharging of aquifer. Groundwater potential zone identified by ERT is verified at one site by drilling a bore well.

1] With time-lapse electrical resistivity tomography (ERT), transport processes in the subsurface can be imaged and monitored. The information content of obtained spatiotemporal data sets opens new ways to characterize subsurface spatial variability. Difficulties regarding a quantitative interpretation of the imaged transport may arise from the fact that data inversion used in ERT is generally underdetermined and that ERT data acquisition is often limited to two-dimensional (2-D) image planes. To address this problem, we conducted a numerical tracer experiment in a synthetic heterogeneous aquifer with preset variability and spatial correlation of the hydraulic conductivity and monitored the tracer breakthrough in a 2-D image plane perpendicular to the mean flow direction using time-lapse ERT. The tracer breakthrough patterns in the image plane were interpreted using equivalent transport models: an equivalent convection dispersion equation to characterize the spatially averaged breakthrough and a stream tube model to characterize local breakthrough curves. Equivalent parameters derived from simulated and from ERT inverted concentrations showed a good agreement, which demonstrates the potential of ERT to characterize subsurface transport. Using first-order approximate solutions of stochastic flow and transport equations, equivalent model parameters and their spatial variability were interpreted in terms of the local-scale dispersion and the spatial variability of the hydraulic conductivity. The spatial correlations of the stream tube velocity and of the hydraulic conductivity were found to be closely related. Consequently, the hydraulic conductivity spatial correlation may be inferred from stream tube velocity distributions, which can be observed with sufficiently high spatial resolution using ERT.

Carbon nanotubes (CNTs) treated by using a mixed solution of H 2 SO 4 and HNO 3 were uniformly dispersed into cement paste by means of ultrasonic energy. Electrical resistivity and pressure-sensitive properties under cyclic compressive loading of this composite were analyzed and compared to that of untreated-CNT reinforced cement paste. Results show that the addition of treated or untreated CNTs to cement paste leads to a notable decrease in volume electrical resistivity and a distinct enhancement in compressive sensitivity. The microstructures of these cement composites were analyzed by using scanning electron microscope. The microscopic observation reveals that both treated and untreated CNTs were dispersed homogenously in the cement matrix. For untreated CNT-reinforced cement composites, the CNTs with glossy surface were zigzag and cling to cement matrix; the bridging of cracks and a well three-dimensional meshwork were also observed. For treated-CNT reinforced cement composites, the surface of CNTs was covered by C-S-H, which leads to a higher mechanical strength. The contact points of the treated-CNTs in composites were much fewer than that of the untreated-CNTs in cement matrix composites, which leads to a higher compressive sensitive properties and a lower electrical conductivity.

A quasi 3D electrical resistivity (ERT) survey was undertaken at a UNESCO World Heritage site, Saqqara, Giza, Egypt, during a joint archaeological-geophysical mission from Cairo University. The main objective is to detect the locations of the subsurface archaeological tombs/or crypts and to allocate any possible archaeological bodies/features buried underneath the study area. In this survey, SYSCAL Pro system with 24 electrodes and a multi-core cable is used for automatic data acquisition of profiling data. The dipole-dipole array was used to enhance resolution, 14 resistivity lines are conducted during this Survey. The processed data were analysed in order to produce resistivity tomography (ERT) for qualitative and quantitative interpretations. Inversion of the ERT data identified variation of resistivity values and the expected locations of the underground galleries and highlight the presence of regular shape structures probably due to features of archaeological interest. Excavations made accordingly in the study area led to an interesting discovery of a tomb of the Great Army General, Iwrhya. The tomb is approximately 2000 years old as it covers the reigns of both Kings Seth I and Ramesses II. Using the 3D resistivity tomography with such a multi-electrode technique proved its efficiency and applicability for non-invasive archaeo-geophysical prospecting.