Electrical Resistivity Tomography Investigations Research Articles

Directional variations of site response in a landslide area using ambient noise analysis via Nakamura’s and polarization-based method

The complexity of the NE Iran region in which the 2014 Nargeschal landslide occurred, increased the necessity of detailed survey on the site response properties of this region. New investigations expanded the set of ambient noise measurements acquired in a previous work on the area affected by mass movement. The outcome of electrical resistivity and geotechnical studies were used to provide a comprehensive model of the landslide in addition to the substratum geology. The ambient noise recordings were analysed using the well-established Nakamura’s method and a recently devised approach based on the analysis of the Rayleigh wave ellipticity to provide more detailed information on site resonance properties characterized by directional variations. The outputs, which were compared with the results of electrical resistivity tomography and geotechnical investigations, showed the better performance of the latter method in terms of stability and reliability of the results. Indeed, it allowed to detect site resonance characteristics that were unrecognizable by the Nakamura’s method. Conclusively, the ambient noise analysis reveals that the directional resonance on different parts are due to the landslide and structural features of the site. The information obtained in this work is relevant for seismic hazard assessment in the study area.

GPR and ERT Investigations in Urban Areas: the Case-Study of Matera (Southern Italy)

This paper deals with a geophysical survey carried out in some critical urban areas of the historical city of Matera (Southern Italy). Matera has a very complex shallower stratigraphy characterized by both anthropic and natural “targets” and is affected by geological instability. Therefore, Matera represents an ideal and very challenging outdoor laboratory for testing novel approaches for near-surface explorations in urban areas. Here, we present the results of a near-surface survey carried out by jointly applying Ground Penetrating Radar (GPR) and Electrical Resistivity Tomography (ERT) methods. The survey was implemented in three different critical zones within the urban area of Matera (Piazza Duomo, Piazza San Giovanni, Villa dell’Unità d’Italia). These test sites are of great interest for archaeological and architectonical studies and are affected by ground instability phenomena due to the presence of voids, cavities and other anthropic structures. The effectiveness of the survey was enhanced by the exploitation of advanced 3D tomographic approaches, which allowed to achieve 3D representation of the investigated underground and obtain information in terms of both the location and the geometry of buried objects and structures and the characterization of shallow geological layers. The results of the surveys are now under study (or have attracted the interest) of the Municipality in order to support smart cities programs and activities for a better management of the underground space.

Application of non-invasive geophysical methods (GPR and ERT) to locate the ancient foundations of the first cathedral of Puebla, Mexico. A case study

This article presents the results of a ground penetrating radar (GPR) and Electrical Resistivity Tomography (ERT) investigation carried out in the atrium of the Cathedral of Puebla to shed new light on the location of the original temple known as the “Old Cathedral”. Historians who endeavor to reconstruct the past of this historical monument propose two hypotheses. To verify whether the foundations are located on the north-west or north-east side of the current cathedral, a GPR study was conducted with 200 and 400 MHz antennas. The study was completed with an ERT survey. The remains of the old cathedral were located and identified in the northwestern part of the atrium. Further anomalies related to subsurface structures and consistent with the ephemeral existence of a smaller temple, the “Sagrario”, were detected. The GPR proved to be the most suitable method to investigate without causing damage suspected subsurface remains, thus protecting cultural heritage.

Geophysical Mapping of Shallow Rock Salt at Borabue, Northeast Thailand

ABSTRACTIn the northeast of Thailand, many swamps and lakes show evidence of rock salt dissolution, with attendant environmental problems due to saline groundwater and soil salinization. The knowledge of the depth and structure of the rock salt would be useful to achieve a better understanding of the impact of its dissolution on the environment and to facilitate effective land management strategies. Geophysical methods can provide key subsurface information. Four seismic refraction profiles and three electrical resistivity tomography profiles were carried out between Nong Bo and Nong Pong reservoirs in the salt‐affected Borabue district of Maha Sarakham province. The seismic results indicate the top of shallow rock salt beneath Nong Bo reservoir as a diagnostic zone of high P‐wave velocity >3400 m/s at depths >20 m. The electrical resistivity tomography investigation shows electrical resistivity values ≳5 Ωm at similar depths, indicative also of shallow rock salt. Zones interpreted to be saline groundwater are electrically conductive, identified by electrical resistivity values ≲5 Ωm in the electrical resistivity tomography images. The combined seismic–electrical resistivity tomography interpretation suggests that shallow rock salt lies beneath the reservoirs and ponds in the Borabue district but does not appear to form a continuous body between the two largest reservoirs.

Optimized electrical resistivity tomography investigation established in identifying pit tombs of Mogareb, a cemetery area in a Pre-Aksumite archaeological site of Seglamen, northern Ethiopia

The larger area of Aksum is known as the most important archaeological areas in northern Ethiopia. It is included in the UNESCO World Heritage List as from about the IV century BC, it developed as one of several polities on the Tigrean plateau and emerged as the capital city of a powerful kingdom roughly between the II and the VIII centuries AD. The Mogareb is a cemetery in a Pre-Aksumite archaeological site of Seglamen located about 12 km South-West of Aksum.The geophysical survey was deployed to investigate the cemetery with the objective of finding and locating unmarked tombs. This work was also intended to test potential of the technique for the wider archaeological area of Aksum, in similar context to Mogareb, where application of geophysical techniques in multidisciplinary archaeological researches, in general, is not common.The approach in this work established an optimized use of the electrical resistivity tomography technique in understanding the archaeological context of the Pre-Aksumite site of Seglamen. The electrical resistivity tomography investigation of large cemetery sites as Mogareb requires a methodological approach designed to define areas of maximum interest where data collection should be planned. Thus, the ERT method suited the Mogareb cemetery area due to the large amount of apriory information from previous archaeological expeditions involving surface collections and excavations that identified and limit extent of the cemetery and were used in the calibration of geophysical survey results.The electrical resistivity tomography survey was conducted on a rectangular grid of 19.5 m by 44.25 m with 0.75 m unit electrode spacing and line spacing in a Dipole-Dipole configuration resulting in high resolvable 2D and 3D electrical resistivity model sections. The models were successful to show interpreted pit tombs anomalies some of which were verified in an excavation of a 10 m by 10 m grid that had an overlap of 6 m by 10 m area to the Northern edge of the electrical resistivity tomography grid.

High-resolution investigation of masonry samples through GPR and electrical resistivity tomography

This paper aims to explore potential and limits of the combined use of ground penetrating radar (GPR) and electrical resistivity tomography (ERT) investigations for the characterization of reinforced masonry samples. To this aim, both techniques were applied on two laboratory small-scale wall samples before and after the application of a shear-compression diagonal load. Laboratory samples (1×1×0.25m) are made of bricks and tuff respectively and reinforced with a thin high-strength and high-conductive fibre fabric. In order to improve the sample-antenna coupling in presence of conductive reinforcements, a Plexiglas plate was added underneath the 2GHz antenna. GPR data were acquired along profiles spaced 0.1m apart and ERT measurements were executed on a 0.1m regular spaced grid with a dipole-dipole array operating in a three-dimensional configuration. GPR datasets were also analysed in non-conventional mode, by means of the picking of the reflection time of the EM wave from the rear face of the samples.Results show that GPR and electrical resistivity tomography were both able to detect fractures and weakness zones caused by the load application, even though with a higher resolution for the georadar with respect to the geoelectrical method. The use of a dielectric material between the GPR antenna and the investigated medium improves substantially the signal penetration in the case of shallow high-conductive layers. Finally, three-dimensional synthetic simulations on the same samples validate the experimental evidences. Therefore, we demonstrate that this approach can be a reliable tool to monitor static load tests and it can be extended to the whole load cycle (before, during and after the experiment).

Saltwater Intrusion Appraisal of Shallow Aquifer in Burutu Area of the Western Niger Delta with 2D Electrical Resistivity Tomography

The area is faced with endemic groundwater quality problems arising from abandoned shallow and deep boreholes. The abandonment of shallow boreholes is presumed to have been caused by saltwater intrusion from the ocean. The objective of this paper is to examine if saltwater is responsible for groundwater degradation associated with shallow groundwater aquifer. To achieve this, a multi-electrodes ABEM SAS 4000 Terrameter was used in the acquisition of 2D electrical resistivity tomography data. Inverse models which estimate actual subsurface geologic resistivity was generated from RES2DINV software and subsequently geologic information were construed from them. The interpretation of the various profiles returned resistivity values which contrasted the existence of saltwater in the pore spaces of groundwater aquifer media in the area under investigation. Resistivity images of values ranged from 2.34Ωm to 70 Ωm where interpreted as clays, greater than 70-90Ωm as fine sand and 90Ωm and above where interpret as medium sand. The evidence revealed by the 2D electrical resistivity tomography investigation combined with geochemistry of groundwater from literature suggested that abandonment of shallow boreholes are probably not related to saltwater intrusion. The study has established that poor groundwater quality being experienced is not caused by saltwater intrusion rather by iron which cannot be separately distinguished from groundwater by resistivity technique. Key Word: 2D electrical resistivity tomography, Burutu, Saltwater intrusion, shallow aquifer, western Niger Delta, groundwater quality

Mapping Lithology and Assessing Recharge Characteristics in a Granitic Hard Rock Aquifer: Inference from 2D Resistivity, Induced Polarization, Tracer and Moisture Measurements

Abstract: Two dimensional Electrical Resistivity Tomography (ERT) investigation along with Time Domain Induced Polarization (TDIP) investigation covering 1.6 km line were carried out at 3 natural recharge sites in a overexploited groundwater granite watershed, situated in a semi arid region in the state of Telangana, India. At these sites, shallow and/or deep moisture influx measurements were also carried out using injected tritium tracer and neutron moisture probe. The watershed is covered by sandy loam to silt loam soil, receives an average annual rainfall of 620 mm with the pre monsoon groundwater level ranging from 8m to 29m bgl. The spot investigations were done to assess and understand the recharge process and groundwater potential in terms of resistivity/conductivity and moisture characteristics of the subsurface rock formation. The measured and 2D inverted resistivity models shows soil, highly weathered and moderately weathered zones up to a depth of 22m followed by semi-weathered and massive granites up to the maximum depth of 78m. The resistivity values of the soil and shallow weathered zones varying between ~5-50 Ohm.m up to a depth of 12m. The large variation in resistivity values of the soil and weathered zone is probably indicative of large variation in the moisture potential. The resistivity models clearly mapped the granitic hard rock structure in the depth range of 22 – 78m, which has a significant resistivity contrast (~1500-11000 Ohm.m) with respect to the overlying semi weathered layers. The modeled 2D resistivity data at a site in two perpendicular directions shows similar geological structure and geoelectric layers. The TDIP dataset shows insignificant chargeability variations (1-7 mV/V) up to the investigated depth of 78m, which probably indicates low to moderate moisture and groundwater potential in the vadoze and saturated zones of the aquifer. The experimental investigations provide scope for assessing dynamic recharge and groundwater potential at selected sites in an overexploited granite watershed in the present geological context.

Investigation of the probable wastewater infiltration and its impact on groundwater quality by electrical resistivity tomography and hydrochemistry: a case study of the Pleistocene aquifer at El Sadat city, Egypt

Electrical resistivity tomography (ERT) and hydrochemical investigations were conducted at the wastewater ponds (oxidation ponds) in El Sadat industrial city, Egypt, to study the possibility of wastewater percolation to the Pleistocene aquifer and its effect on the groundwater chemistry. Pleistocene aquifer is the main groundwater reservoir in this area, where El Sadat city and its vicinities use it as a main source for water supplies required for drinking, agricultural and industrial activities. In this study, seven ERT profiles were measured around the wastewater ponds and ten water samples were collected from the ponds and the nearby groundwater wells. The water samples were analyzed for major cations (Ca2+, Na+, K+, and Mg2+); major anions (Cl−, \( {\text{CO}}_{ 3}^{ - 2} \), \( {\text{HCO}}_{ 3}^{ - } \), \( {\text{SO}}_{ 4}^{ - 2} \)), nutrients (\( {\text{NO}}_{ 2}^{ - 1} \), \( {\text{NO}}_{ 3}^{ - 1} \), and \( {\text{PO}}_{ 4}^{ - 3} \)) and heavy elements (Cd, V, Cr, Zn, Ni, Cu, Fe, Mn, and Pb). Also, the physical parameters (pH, alkalinity, EC, and TDS) of the water samples were measured. The ERT sections exhibited low resistivity values towards the wastewater ponds and high values in opposite sides. Besides, the water table was detected at shallow depths towards the oxidation ponds. These indications could verify the possibility of wastewater infiltration to the groundwater aquifer around the oxidation ponds. Comparison of the physicochemical parameters of the wastewater samples with those of the groundwater samples indicates that the ionic levels are randomly varying and no specific trend could be obtained. Also, the wastewater samples show some ionic levels lower than those detected in the nearby groundwater samples. Besides, the nitrate level is higher in the water samples collected from the cultivated land than the wastewater samples. From this study, it could be concluded that the wastewater infiltrated from the oxidation ponds is NOT the main controller of the groundwater chemistry of the Pleistocene aquifer in this area. Rather, the variable ionic concentrations could be attributed to local, natural and anthropogenic processes.

Monte Cotugno Dam Monitoring by the Electrical Resistivity Tomography

This work presents an interesting case-study regarding a big dam monitoring thanks to the deployment of the electrical resistivity tomography (ERT). In particular, we are concerned with the largest rock-fill dam in Europe, i.e., the dam on Sinni river in Basilicata region (Italy), which is one of the main civil strategic infrastructures in Southern Italy. The presence of fractures visible on the hanging waterproof dam has motivated the investigation about the possible water infiltration in the dam. ERT surveys were carried out to detect the inner areas characterized by lower electrical resistivity values as indicators of the undesired presence of water inside the structure. The imaging capability of the ERT investigation was the key to detect and localize the areas of the dam affected by the presence of water. On the basis of ERT results, the managing body of the dam activated other diagnostic tools in view of a proper planning of future restoration works.

Stratigraphy, structure, and volcano-tectonic evolution of Solfatara maar-diatreme (Campi Flegrei, Italy)

This study focuses on the Solfatara volcano within Campi Flegrei, a volcanic field located on the Tyrrhenian coast of southern Italy. Volcanism at the Campi Flegrei caldera has included phreatic to phreatomagmatic explosions and both magmatic (ranging from small scoria-producing events to those with Plinian columns) and effusive eruptions. These eruptions have formed tuff cones, tuff rings, minor scoria cones, and lava domes. A detailed stratigraphic, structural, and geophysical study of the area indicates that the Solfatara volcano is a maar-diatreme structure previously not recognized within the Campi Flegrei caldera. It is characterized by a crater cut into earlier volcanic deposits, a small rim of ejecta, and a deep structure (down to 2–3 km). This maar-diatreme has allowed the gases and fluids to flow up to the surface over a long time. A new geological map and cross sections show a complex architecture of different volcano-tectonic features including scoria cones, lavas, cryptodomes, feeder dikes, pipes, ring and regional faults, and explosive craters. Volcanological data were collected with the main aim of characterizing the eruptive activity in a limited sector of the caldera. Fault and fracture analyses, using the scan line methodology, highlight the role of the main structures that accompanied the volcanic evolution within this sector of the Campi Flegrei caldera. To better constrain the subsurface structure of the Solfatara crater, electrical resistivity tomography investigations were integrated with the volcano-tectonic information. All data suggest that the Solfatara area is dominated by a maar-diatreme evolution. Presently, the Solfatara area shows widespread hydrothermal and fumarolic activity that is localized along the major faults. The results allow us to define a particular type of volcanic activity in the recent past, in what is still considered today an area with a higher probability of opening new vents, particularly for possible phreatic activity.

Integrated Geophysical and Hydrochemical Approach for Locating Fresh Water Locations in a Coastal Terrain

An integrated geophysical investigation viz., Vertical Electrical Sounding (VES), Electrical Resistivity Tomography (ERT) and Ground Penetrating Radar (GPR) were carried out in a coastal terrain at Vizag Steel Plant (VSP), Visakhapatnam, Andhra Pradesh., India for locating fresh water locations. The entire area was underlain by recent alluvial of varying thickness consists of sand, clay and silt with basement as Kondalite rock formation consisting of saline water in some parts of the area. Locating favorable groundwater locations in such a terrain is a difficult task. The area consists of saturated clay, saturated silt and saline water has the same resistivity signature and misleads resistivity data interpretation for identifying and recommending the suitable groundwater locations in a coastal terrain. To overcome these uncertainties, a second geophysical approach or combinations of geophysical methods become necessary to resolve these resistivity ranges in a more reliable and better fruitful interpretation of sub-surface layers. In order to pin-point the groundwater locations at VSP; VES, ERT and GPR investigations were carried out. Interpreted results of VES, ERT pseudo-section and GPR images (radargram) were correlated with each other to ascertain confidently the geophysical signature of the sub-surface. Combination of geophysical methods gives better resolution or interpretation of sub-surface information before made any recommendations for drilling of borewell. Based on integrated geophysical investigation few borewell sites were recommended and drilled. The observed drilled lithologs was well correlated with the VES, ERT and GPR data. Besides, this hydrochemical analysis of water samples was carried out from the existing borewells and dugwells. Total Dissolved Solids (TDS) and chloride concentration were ranges from 189 to 3398 mg/l and 5 to 1610 mg/l. The eastern and north-eastern part of the area has elevated concentration of TDS and chloride indicating intrusion of saline water. TDS concen- tration of drilled borewell was found to range from 400 to 500 mg/l. The observed yield of drilled borewells ranges from 104 to 3623 gal/hr.

Electrical resistivity tomography investigations along the planned dykes of the HPP Brežice water accumulation basin

Geophysical investigations were conducted using electrical resistivity tomography (ERT) along planned dykes of the HPP Brežice water accumulation basin. The ERT profile is 7.3 km long and is located on the right riverbank of the Sava River on the Kr{ko-Brežice field (E Slovenia). A purpose of the investigations was to determine a boundary between semipermeable Miocene and permeable Plio-Quaternary (Pl-Q) and Quaternary (Q) sediments for the proper design of the jet grouting sealing curtain, which will prevent lateral outflow of water from the accumulation basin. In this paper we present processing of the section between 5100 and 6100 m of the profile line. In this section the measurement template was set to 25 depth levels, because a significant increase in a thickness of the Pl-Q sediments was expected. Modelling of the measured apparent electrical resistivity data was carried out with RES2DINV and RESIX 2DI inversion software. Different inversion parameters were used to create 15 geoelectrical models for each program, which were then compared and evaluated based on borehole data and on previous geological investigations of the area. With the final geoelectrical models it was possible to successfully determine areas of three expected stratigraphic members and limit an electrical resistivity range for each one of them. The boundary is well defined between Q and Pl-Q and also between Q and Miocene sediments with sharp contrast in electrical resistivity between them. A boundary between Pl-Q and Miocene sediments was not that obvious, but it was possible to determine its shape by the use of different inversion parameters. We propose a simplified geological cross section based on the interpreted geoelectrical models and borehole data.

Prospecting for clay minerals within volcanic successions: Application of electrical resistivity tomography to characterise bentonite deposits in northern Sardinia (Italy)

Electrical resistivity tomography (ERT) is applied to prospect for and characterise a bentonitic clay deposit in northern Sardinia. Sardinian bentonites derived from the hydrothermal alteration of thick successions of pyroclastic flows and epiclastites are associated with the Oligo-Miocene calc-alkaline volcanic cycle. The alteration of these rocks is generally controlled by faults that control the local circulation of hydrothermal fluids. Two-dimensional ERT investigations were performed close to a faulted area to define the location, thickness and lateral continuity of the clayey body, and determine how it relates to faulting and stratigraphy. A line-based three-dimensional ERT data acquisition was carried out in a selected area to estimate the available clay reserves. The reliability of these resistivity models was assessed by comparison with local borehole data. Finally, the interpretation of the ERT results was optimised through synthetic modelling of the electrical resistivity imaging technique. The results define the extent and geometry of the bentonitic deposit with good accuracy and outline the scenarios where the ERT method may provide optimal results when prospecting for clay deposits.

Electrical resistivity tomography investigations on a paleoseismological trenching study

Two-dimensional electrical resistivity tomography (ERT) investigation was performed in a paleoseismological trenching study. Data acquisition strategies such as the selection of electrode configuration and electrode intervals of ERT application were investigated in this paper. The ERT results showed that the Wenner and Wenner–Schlumberger arrays yielded similar results for subsurface characteristics whereas the DD array provided slightly different results. The combined usage of these arrays produced satisfactory images of the subsurface resistivity distribution. In addition, the electrode spacing tests revealed that a suitable interpretation of subsurface geology can be obtained from a 5 m electrode interval. However, a suitable trenching location defined by successful 2D resistivity models was obtained for 1 m electrode spacing. Therefore, the comparison of the trench and ERT results was also possible. The results of trenching and ERT studies substantially support each other.

Investigating a damaging buried sinkhole cluster in an urban area (Zaragoza city, NE Spain) integrating multiple techniques: Geomorphological surveys, DInSAR, DEMs, GPR, ERT, and trenching

This contribution analyses a complex sinkhole cluster buried by urban elements in the mantled evaporite karst of Zaragoza city, NE Spain, where active subsidence has caused significant economic losses (~0.3million Euro). The investigation, conducted after the development of the area, has involved the application of multiple surface and subsurface techniques. A detailed map of modern surface deformation indicates two active coalescing sinkholes, whereas the interpretation of old aerial photographs reveals the presence of two additional dormant sinkholes beneath human structures that might reactivate in the near future. DInSAR (Differential Interferometry Synthetic Aperture Radar) displacement data have limited spatial coverage mainly due to high subsidence rates and surface changes (re-pavement), and the Electrical Resistivity Tomography (ERT) and trenching investigations were severely restricted by the presence of urban elements. Nonetheless, the three techniques consistently indicate that the area affected by subsidence is larger than that defined by surface deformation features. The performance of the Ground Penetrating Radar (GPR) technique was adversely affected by the presence of highly conductive and massive anthropogenic deposits, but some profiles reveal that subsidence in the central sector of one of the sinkholes is mainly accommodated by sagging. The stratigraphic and structural relationships observed in a trench dug across the topographic margin of one of the sinkholes may be alternatively interpreted by three collapse events of around 0.6m that occurred after 290yr BP, or by progressive fault displacement combined with episodic anthropogenic excavation and fill. Average subsidence rates of >6.6mm/yr and 40mm/yr have been calculated using stratigraphic markers dated by the radiocarbon method and historical information, respectively. This case study illustrates the need of conducting thorough investigations in sinkhole areas during the pre-planning stage including a geomorphic approach. A sound geomorphic model is essential for the proper design of the site investigation, the interpretation of the data and application of effective mitigation measures. Once sinkhole areas are developed, urban elements largely restrict the applicability and performance of multiple techniques, substantially decreasing the feasibility and benefit/effort ratio of the investigations.

Electrical resistivity tomography monitoring studies at Balçova (Turkey) geothermal site

ABSTRACTThis investigation examines the electrical resistivity tomography (ERT) monitoring performed at geothermal sites. It includes two phases of time‐lapse ERT studies of the shallow geothermal liquid transportation that results from the circulation of injected and re‐injected liquids: synthetic modelling and field surveys. The synthetic modelling stage indicated that the injection process in the horizontal layered environment could cause temporal variations. The field investigation was performed between March 2010 and February 2011 at the Balçova geothermal site, Izmir‐Turkey, which has supplied in‐house heating since the 1990s. The time‐lapse ERT investigations were performed on a shallow aquifer system near two boreholes used as injection and re‐injection. In this study, the percentage changes in the synthetic models were determined and compared to the observed inverted time‐lapse monitoring data. We propose that time‐lapse inversion results are more reliable than the standard inversion approximation. However, the resistivity artefacts were significant, and were dependent on the selection of the comparison model and the inversion parameters. Also the selection of the initial model was shown to be the most important step in constraining the later temporal datasets. During the monitoring period, we observed very substantial decreases in the resistivity of time‐lapse results. We conclude that these observed decreases are a result of subsurface temperature or salinity changes associated with the hydrothermal system and fault zone. As a result, this study indicates that time‐lapse studies could be important in the characterisation of the subsurface changes that are connected with geothermal operations and climatic fluctuations.

Application of electrical resistivity tomography methods for delineation of groundwater contamination and potential zones

Identification of damages/changes that are affecting the underground water quality due to the effect of anthropogenic activities is often done after environmental problems have become evident or water portability being strongly affected. Two main applications of electrical resistivity tomography (ERT) methods have been addressed covering characterization of leachate movement from a composting area of a Sugar Mill in Southern India. Good correlation has been obtained between ERT and groundwater quality assessments as well as from groundwater monitoring data sets. The study helped in conceptualization of hydrogeologic framework in basaltic terrain. Impacts on groundwater regime associated with urbanization and industrialization can easily be assessed through the variation of resistivity in the inverse resistivity pseudo-section model of the ERT investigations. Assessment of groundwater potential in an upcoming Urban Node, Greater Hyderabad city has been illustrated in the second example. Identification of good thickness of weathered regolith for location of water harvesting through Green Fingers evolved. The small infrastructure would help carrying of enhanced surface runoff as well as to sustain groundwater yield in the urban node and thereby ensuring sustainable groundwater resource exploitation. The above studies have illustrated immense potential of the ERT tools in the assessment of groundwater contamination as well as groundwater potential.

Electrical resistivity tomography investigation of coseismic liquefaction and fracturing at San Carlo, Ferrara Province, Italy

<p>Massive surface fracturing and sand ejection took place during the main shock of the May 20, 2012, earthquake (Ml = 5.9) in the Emilia-Romagna region, northern Italy. These phenomena were induced by the liquefaction of water-saturated sand layers, and they damaged several buildings, as well as many roads and sidewalks. They were clustered between the villages of Sant'Agostino and Vigarano Mainarda, located along a paleo-reach of the Reno River [Papathanassiou et al. 2012, this volume]. The subsurface surrounding two major (several decameters long) ground ruptures was investigated using electrical resistivity tomographies (ERT), as resistivity is strongly affected by the chemico-physical conditions of loose sediments. Italian regulations require the Municipalities within seismically active areas to develop maps of the potential liquefaction risk. Not all of the territories that are under this kind of risk have been investigated to date. A strong effort to improve this knowledge is therefore needed. Noninvasive geophysical methods can help to fill this gap, as high-resolution techniques are available with good result-to-cost ratios. Among the available methodologies, the most suitable are the methods based on electrical resistivity and permittivity, as they are highly sensitive to the presence of underground water. The ERT method has been carried out successfully across active faults, providing crucial paleoseismological information [Caputo et al. 2003, 2007]. […]</p>

Joint application of geophysical methods and Direct Push-soil gas surveys for the improved delineation of buried fault zones

This study provides an example of fault structure delineation using both geophysical measurements and soil-gas surveys. Seismic refraction and electrical resistivity tomography investigations were performed in combination with Direct Push (DP) soil gas concentration measurements, with the main objective being the characterization of an assumed permeable fault structure which is covered by sediments that are over 20 m thick. Geophysical methods were used to locate a potential fault zone and to provide an insight into the structural features of the covering sediments. Methods for quantifying the soil-gas concentration were applied to evaluate the permeability of the fault zone. The positioning of gas sampling points was based on results of a geophysical survey undertaken beforehand. Gas sampling was performed using DP-technology to obtain concentration profiles for the inert gas Radon-222 and its carrier gas CO2 along the profile at different depths. Joint interpretation of the spatial distribution of geogenic gases and results from the geophysical survey allowed us to produce a representative model image of the fault structure consisting of two fault branches. Based on this image, it was possible to interpret the observed gas concentration patterns.