Academic literature on the topic 'Geoelectrical methods'

Submitted by Francisco Carlos Da Silva (fracarlos@hotmail.com) on 2018-10-22T16:30:22Z No. of bitstreams: 1 Tese -Repositorio final.pdf: 26926264 bytes, checksum: 56e13a425183936436178060a6f5c834 (MD5)<br>Approved for entry into archive by Lucimara Kurokawa Shinoda null (lucimaraks@sorocaba.unesp.br) on 2018-10-23T17:48:36Z (GMT) No. of bitstreams: 1 silva_fc_dr_soro.pdf: 26926264 bytes, checksum: 56e13a425183936436178060a6f5c834 (MD5)<br>Made available in DSpace on 2018-10-23T17:48:36Z (GMT). No. of bitstreams: 1 silva_fc_dr_soro.pdf: 26926264 bytes, checksum: 56e13a425183936436178060a6f5c834 (MD5) Previous issue date: 2018-08-24<br>Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)<br>Os metais potencialmente tóxicos se acumulam frequentemente na zona não saturada do solo e quando em concentrações elevadas podem afetar tanto a biota quanto o aquífero freático. Neste trabalho foram avaliadas as concentrações de metais potencialmente tóxicos no solo do setor mais antigo da necrópole Nossa Senhora Aparecida na cidade de Piedade, SP. O estudo foi desenvolvido durante o período de 2015 a 2018. Inicialmente, foram realizados ensaios geofísicos utilizando as técnicas de Eletrorresistividade (equipamentos Syscal e Ohmmapper) e Eletromagnética Indutiva, com o objetivo de se localizar e dimensionar potenciais sítios anômalos. Após a interpretação dos resultados geofísicos, foram realizadas sondagens para coletas de amostras de solo nos sítios indicados por estas técnicas. As sondagens foram limitadas a três metros de profundidade com amostras coletadas a cada 0,5 m. Nas amostras foram quantificados por espectrometria de emissão óptica com plasma indutivamente acoplado ICP-OES os metais: bário, cádmio, chumbo, cobalto, cromo, cobre, manganês, molibdênio, níquel e zinco. Foram efetuados também os ensaios físicos do solo: granulometria, textura e permeabilidade com carga constante, estes visando compreender o comportamento e mobilidade dos metais. Os resultados das análises químicas indicaram um aumento na concentração, em relação a área de controle (background local) e em algumas profundidades esses aumentos ultrapassam os valores de referência e prevenção estabelecidos pela CETESB/16, dos metais Pb, Co, Cr , Co, Ni, Ba e Zn. O elemento Mo apresentou valores abaixo das orientações da CETESB/2016 mas com valores elevados em relação a área de controle e o Mn, apesar de estar muito elevado se comparado ao controle, não existe até o presente, valores de referência e prevenção estabelecidos pela CETESB/2016. A análise textural e granulométrica indicaram um solo não muito propício para sepultamentos (k = 10-4) segundo as normas brasileiras, mas, para uma avaliação mais criteriosa, devemos considerar as condições geoambientais locais (geomorfologia, pedologia, clima, ciclo hidrológico) e a profundidade do aquífero freático.<br>Potentially toxic metals are often accumulate in the unsaturated zone of the soil and when they are found in a high concentration can affect biota as much as the water's system/ Aquifer. In this work it was evaluated the potentially toxic metals concentration in the soil of the oldest sector of the necropolis Nossa Senhora Aparecida at the city Piedade, SP. The study was developed between 2015 and 2018. At first geophysical tests were done using the techniques of Elecal Resistivity, Ohmmapper Eletrorescence and Inductive Electromagnetic with the objective of locating and dimensioning potential anomalous sites. After an interpretation of the geophysical results soundings were done to collect samples of soil techniques in the areas indicated by this technique. The sounding were limited to three meters deep with samples collected every 0.5 m. The samples were quantified by ICP-OES inductively coupled plasma optical emission spectrometry: barium, cadmium, lead, cobalt, chromium, copper, manganese, molybdenum, nickel and zinc. Also were carried out Soil physical tests: granulometry, texture and permeability with constant load, aiming to understand the behavior and mobility of the metals. The results of the chemical analyzes indicate an increase of the concentration, in relation to the control area (local background) and in some depths these increases exceed the reference and prevention values established by CETESB / 16, metals Pb, Co, Cr, Co, Ni, Ba and Zn. The Mo element presented values below the CETESB / 2016 guidelines but with high values in relation to the control area and the Mn, although it is very high when compared to the control there are no reference and prevention values established by CETESB / 2016. The textural and granulometric analysis indicated a soil not very suitable for burials (k = 10-4) according to the Brazilian standards, but for a more careful evaluation we should consider local geoenvironmental conditions (geomorphology, pedology, climate, hydrological cycle) and the depth of the water table.<br>CAPES: 001

The Iberian Peninsula is considered as a “micro-continent”, located between the Eurasian and the African plates. Several ranges formed during the Alpine orogeny, in the borders of the plate or intraplate. As part of this thesis the first magnetotelluric (MT) data was collected across the intraplate Iberian fold and thrust belt and the first long-period magnetotelluric was collected across the Cantabrian Mountains, located in the northern boundary of the Iberian plate. This MT data was used to image the electrical conductivity distribution of the crust beneath these two orogens. The analysis of the MT data revealed the presence of three-dimensional structures in both studied areas and therefore 3-D inversion algorithms were used to obtain the final resistivity models. In the Cantabrian Mountains the correlation between the geoelectric image, the existing geophysical models and the surface geology provided a deeper understanding of the lithospherical processes. The final model shows excellent correlation with the superficial geology, depicting the main faults and lithologies at depth. The Duero Basin sediments are well delineated. A thickness of 2.5 to 3.5 km was deduced, and is in agreement with the seismic studies and well log data. Conductive zones in the Palaeozoic basement are related to enhanced permeability along the main Alpine faults. These conductive zones detected in the model do not reach more than 10 km in the southern part of the Cantabrian Mountains and 15 km in the northern part, and are therefore concentrated in the upper crust. The hydration/serpentinization of the upper mantle within the mantle wedge and beneath the Moho of the Cantabrian Margin is imaged as a zone of low resistivities. In the Iberian Chain the 3-D inversion model indicates that several Alpine thrusts are imaged as dipping conductors, which are limited to the upper crust. Two of them are the North Iberian Thrust and the Serranía de Cuenca Thrust, which bound to the north and to the south respectively the basement involved areas of the Iberian Chain. Both faults do not reach more than 15 km depth, suggesting that they are linked to the thrust system detachment at 10–15 km depth. This indicates that the Cenozoic thrust system causing the crustal thickening of the Iberian Chain is concentrated in the upper crust, which confirms the previous geological hypothesis proposed by Guimerà and Alvaro (1990). The 3-D inversion model is consistent with the collocated seismic image. A statistical analysis of the correlation between seismic velocity and electrical resistivity along a NE-SW profile is carried out for the upper crust and shows a clear correlation between both parameters. An increase in both seismic velocity and electrical resistivity is observed and is related to the depth at which the geological formations are located.<br>La Península Ibérica es un micro continente situado entre las Placas Euroasiática y Africana. Existen varios orógenos alpinos situados en el borde de placa y en su interior. En esta tesis se han realizado perfiles de magnetotelúrica a través de dos de estos orógenos: la Cordillera Cantábrica y la Cadena Ibérica. A partir de los datos de magnetotelúrica se han obtenido las imágenes de resistividad eléctrica a escala litosférica en la Cordillera Cantábrica y a escala cortical en la Cadena Ibérica. En ambos casos el análisis de la dimensionalidad de la estructura geoléctrica ha puesto de relieve un comportamiento 3-D. Por tanto se han realizado en cada caso inversiones 3-D conjuntas de las cuatro componentes del tensor de impedancias y de la función de transferencia geomagnética. En la Cordillera Cantábrica, la correlación de la distribución de resistividad eléctrica con otros modelos geofísicos y la geología de superficie ha conducido a una mejor comprensión de los procesos litosféricos de formación de la cordillera. El modelo de resistividades obtenido da una imagen de las principales fallas y estructuras en profundidad. La Cuenca del Duero está formada por sedimentos con un espesor variable, entre 2.5 a 3.5 km. El basamento paleozoico resistivo presenta zonas de conductividad elevada relacionadas con las fallas alpinas que no superan los 10 km de profundidad en la parte más meridional de la Cordillera y los 15 km en la parte septentrional de la misma, lo que indica que se sitúan en la corteza superior. La hidratación /serpentinización en la cuña del manto del margen cantábrico aparece reflejada por una zona de elevada conductividad eléctrica. En la Cadena Ibérica el modelo de inversión 3D obtenido revela la geometría de los cabalgamientos alpinos mediante zonas de elevada conductividad. Los dos principales son el Cabalgamiento Frontal Noribérico y el de la Serranía de Cuenca que limitan, al Norte y al Sur respectivamente, el basamento de la Cadena Ibérica. Ambas fallas no superan los 15 km de profundidad, indicando que el sistema de cabalgamientos cenozoico causante del engrosamiento de la cadena se concentra en la corteza superior. Se ha realizado un análisis estadístico de la correlación entre el modelo de resistividades obtenido y un modelo de velocidades sísmicas existente. El resultado indica una coincidencia entre un aumento de velocidades sísmicas y un aumento de resistividad eléctrica relacionado con la localización de las formaciones geológicas a distintas profundidades.

Este trabalho trata do estudo detalhado e com profundidade das metodologias de aquisição, processamento e interpretação de dados de caminhamentos elétricos, sob o enfoque de investigações voltadas a objetivos rasos. Nas técnicas de aquisição 2D (caminhamentos) foram utilizados os arranjos dipolo-dipolo, pólo-dipolo, pólo-pólo e Wenner, permitindo comparações quanto à eficácia dos mesmos. Foi testada uma genuína aquisição 3D utilizando o arranjo pólo-pólo, avaliando-se suas potencialidades e limitações. O Schlumberger foi o arranjo empregado para a execução de SEVs que auxiliaram na interpretação e quantificação das seções geoelétricas 2D, principalmente no que se refere à distribuição vertical das resistividades. Os modelos geoelétricos 2D foram obtidos com um programa de inversão de dados (RES2DINV) que, em tese, é capaz de corrigir as distorções observadas nas pseudo-seções de resistividade elétrica aparente correspondentes aos diversos arranjos utilizados no trabalho. Estes modelos constituem imagens que apresentam uma melhor correspondência com a realidade geológica em subsuperfície, o que facilita a interpretação dos resultados. Procurou-se explorar o máximo as potencialidades do programa de inversão, visando a obtenção de imagens de boa qualidade. A interpretação geofísica foi sempre efetuada com base em informações diretas disponíveis (furos de sondagem, trincheiras, poços e afloramento). Em uma escala de investigação rasa, a resolução passa a ter uma importância fundamental. Procurou-se demonstrar que, quando são utilizados pequenos espaçamentos entre eletrodos (menores que quatro metros), particularmente no caso do dipolo-dipolo, é possível a execução de mais níveis de investigação em profundidade (superiores a oito) ainda com uma boa qualidade do sinal. Por outro lado, os arranjos dipolo-dipolo e pólo-pólo permitem um número muito maior de níveis de investigação sem a limitação das pequenas aberturas, mas com alguma perda em definição. Como conseqüência, tem-se um significativo aumento na quantidade de dados gerados na seção, o que contribui para o incremento da resolução bi-dimensional. Outro aspecto testado e avaliado foi o da utilização de múltiplos espaçamentos entre eletrodos sobre o mesmo perfil de levantamento. Este interessante procedimento garante, além de resolução nas porções rasas (graças aos espaçamentos pequenos), o alcance de maiores profundidades de investigação (devido aos espaçamentos maiores) em uma mesma seção. A eficácia desta prática foi verificada tanto na construção das pseudo-seções, como nos modelos geoelétricos gerados pela inversão dos dados (modelagem). A metodologia foi testada em três distintas áreas tendo por objetivo o mapeamento de um nível d´água raso, a determinação da profundidade e conformação de topo rochoso e o mapeamento de uma provável pluma de contaminação. Além de uma ampla revisão bibliográfica sobre o assunto, foi também abordado neste trabalho o controverso tema da profundidade de investigação que de fato se verifica com os arranjos de eletrodos comumente empregados em eletrorresistividade. Procurou-se, com esta tese, contribuir para um melhor entendimento acerca do tema \"imageamento geoelétrico\" e alguns tópicos a ele relacionados, quais sejam: arranjo de eletrodos, procedimentos para se conseguir um bom volume de dados na seção, utilização eficiente do programa de inversão que gera os modelos e, finalmente, a interpretação dos resultados sempre balizada por informações diretas disponíveis e por outros métodos ou técnicas geofísicas de apoio.<br>This paper addresses a detailed, in-depth study on data aquisition, processing and interpretation methodologies for 2D electrical profilings, focusing on investigations oriented to shallow targets. Two-dimensional (electrical profilings) acquisition techniques were used on a wide range of arrays - dipole-dipole, pole-dipole, pole-pole and Wenner arrays - for efficiency comparison purposes. A real 3D acquistion was tested with the pole-pole array in order to check its potential use and limitations. Schlumberger was the array used for SEVs, which helped to interpret and quantify 2D geoelectrical sections, especially as to the vertical distribution of resistivity. The 2D geoelectrical models were generated with an inversion computer program (RES2DINV), which basically corrects any distortions found in the apparent resistivity pseudosections corresponding to the arrays included in this study. These models create images that better match the subsurface geological reality, therefore simplifying the interpretation of results. We tried to explore the full potential use of the inversion computer program for good quality images. The geophysical interpretation was always based on the subsurface information available (boreholes, trenches, wells and outcrop). Resolution is critical in a shallow investigation scale. This study tried to show that the use of small spacings between electrodes (less than four meters), particularly in dipole-dipole arrays, allows for more in-depth investigation levels (greater than eight) without compromising signal quality. On the other hand, dipole-dipole and pole-pole arrays allow for a larger number of investigation levels without small spacings limitations, but with a slight loss of definition. Consequently, there is a significant increase in the amount of data generated at the section, enhancing 2D resolution. Another aspect tested and assessed was the use of multiple spacings between electrodes on the same survey profile. In addition to resolution in shallow sections (thanks to small spacings), this interesting procedure allows deeper investigation levels (due to larger spacings) in the same section. The efficacy of this practice was verified both in the development of pseudo-sections and in the geoelectrical models generated by inversion modelling. The methodology was tested in three different areas in order to map a shallow water table, determine the depth and shape of the bedrock, and map a potential contaminant plume. In addition to the broad literature review available, this paper also covered the controversial topic of depth investigation actually present in electrode arrays typically used in electrical resistivity methods. This thesis tried to provide a better understanding of \"geoelectrical resistivity imaging\" and related topics such as: electrode array, procedures required to generate good volumes of data in the section, efficient use of the inversion computer program behind the models and, lastly, interpretation of results, always based on the subsurface information available and on other supporting geophysical methods or techniques.

Orientador: Chang Hung Kiang<br>Banca: Walter Malagutti Filho<br>Banca: Vagner Roberto Elis<br>Resumo: Visando caracterizar assinaturas geoelétricas em áreas contaminadas por hidrocarbonetos de petróleo, foram realizados levantamentos geofísicos utilizando-se os métodos da eletrorresistividade e análises hidroquímicas em área localizada no Pólo Industrial de Cubatão - SP. Foram realizadas 19 sondagens elétricas verticais (SEVs), 4 imageamentos elétricos 2D e 3 imageamentos elétricos 3D, tendo sido identificadas, por meio destas técnicas, 12, 21 e 9 anomalias, respectivamente. Constatou-se que a presença de anomalias condutivas na zona não saturada coincide com a ocorrência de fase livre nos poços de monitoramento. A identificação de NH4 +, subjacente à ocorrência de fase livre, confirmou a atuação de processo de denitrificação. As baixas concentrações dos íons sulfato (SO4 2-) e ferroso (Fe2+) indicam que os mesmos foram reduzidos biologicamente para sulfeto (S2-) e precipitado como sulfeto de ferro (FeS), respectivamente. Esses resultados permitem concluir que as anomalias condutivas estão diretamente associadas à presença de fase residual de hidrocarbonetos, em processo de biodegradação, na zona não saturada. Desta forma, os métodos de investigação geofísica utilizados permitiram identificar áreas sob influência de hidrocarbonetos de petróleo.<br>Abstract: Geophysical surveys using electroresistivity methods and hydrochemical analyses were applied aiming the characterization of geoelectrical signatures in hydrocarbon contaminated sites located in the Polo Industrial de Cubatão - SP. There have been accomplished nineteen vertical electric soundings (VESs), four 2D and three 3D electrical imaging, which identified 12, 21 and 9 geophysical anomalies respectively. It was verified that the presence of conductive anomalies within the non-saturated zone coincided with the occurrence of free phase on the monitoring wells. Ammonium (NH4 +) identification, underlying the free phase occurrence, reinforced the activity of denitrifying process. Additionally, low concentration values of sulfate (SO4 2-) and ferrous (Fe2+) ions indicated that they were, respectively, biologically reduced to sulfide (S2-) and precipitated as iron sulfide (FeS). Based on those results, it was concluded that the conductive anomalies detected inside the non-saturated zone were directly associated with the presence of hydrocarbon residual phase, with was undergoing a biodegradation process. Therefore, the geophysical methods applied in this study allowed the identification of sites under petroleum hydrocarbons influence.<br>Mestre

Made available in DSpace on 2014-06-11T19:26:12Z (GMT). No. of bitstreams: 0 Previous issue date: 2007-09-13Bitstream added on 2014-06-13T18:54:18Z : No. of bitstreams: 1 baessa_mpm_me_rcla.pdf: 2451214 bytes, checksum: 3876fa480ca0e2bb77803a47b1630c54 (MD5)<br>Visando caracterizar assinaturas geoelétricas em áreas contaminadas por hidrocarbonetos de petróleo, foram realizados levantamentos geofísicos utilizando-se os métodos da eletrorresistividade e análises hidroquímicas em área localizada no Pólo Industrial de Cubatão – SP. Foram realizadas 19 sondagens elétricas verticais (SEVs), 4 imageamentos elétricos 2D e 3 imageamentos elétricos 3D, tendo sido identificadas, por meio destas técnicas, 12, 21 e 9 anomalias, respectivamente. Constatou-se que a presença de anomalias condutivas na zona não saturada coincide com a ocorrência de fase livre nos poços de monitoramento. A identificação de NH4 +, subjacente à ocorrência de fase livre, confirmou a atuação de processo de denitrificação. As baixas concentrações dos íons sulfato (SO4 2-) e ferroso (Fe2+) indicam que os mesmos foram reduzidos biologicamente para sulfeto (S2-) e precipitado como sulfeto de ferro (FeS), respectivamente. Esses resultados permitem concluir que as anomalias condutivas estão diretamente associadas à presença de fase residual de hidrocarbonetos, em processo de biodegradação, na zona não saturada. Desta forma, os métodos de investigação geofísica utilizados permitiram identificar áreas sob influência de hidrocarbonetos de petróleo.<br>Geophysical surveys using electroresistivity methods and hydrochemical analyses were applied aiming the characterization of geoelectrical signatures in hydrocarbon contaminated sites located in the Polo Industrial de Cubatão – SP. There have been accomplished nineteen vertical electric soundings (VESs), four 2D and three 3D electrical imaging, which identified 12, 21 and 9 geophysical anomalies respectively. It was verified that the presence of conductive anomalies within the non-saturated zone coincided with the occurrence of free phase on the monitoring wells. Ammonium (NH4 +) identification, underlying the free phase occurrence, reinforced the activity of denitrifying process. Additionally, low concentration values of sulfate (SO4 2-) and ferrous (Fe2+) ions indicated that they were, respectively, biologically reduced to sulfide (S2-) and precipitated as iron sulfide (FeS). Based on those results, it was concluded that the conductive anomalies detected inside the non-saturated zone were directly associated with the presence of hydrocarbon residual phase, with was undergoing a biodegradation process. Therefore, the geophysical methods applied in this study allowed the identification of sites under petroleum hydrocarbons influence.

碩士<br>國立中央大學<br>應用地質研究所<br>86<br>Detection of Subsurface Contamination by Using Integrated Geoelectrical MethodsShan-wen SuABSTRACTIntegrated geoelectrical methods was applied to study the subsurface contamination by measuring subsurface electrical anomalies caused by contamination plumes. This study can be divided into two parts ; (1) an investigation of the spatial and temporal leakage of LNAPL from pipeline at Nankansite after an immediate remedy, and (2) the potential of geoelectrical methods applied to mapping the areal extent of pollution in a simulation experiment. In the former case, the direct resistivity re-sults were measured at different time intervals for comparison with each other. With an aid from former resistivity data and current variation of groundwater levels, the migration of subsurface the subsurface residual can be figured out. As for the simulation experiment, a real time leakage detecting system was established by using deployed different elec-trodes around the presumed pipe leakage point , the abilities of detection of leakage by different geoelectric methods were further evaluated. Some conclusions are drawn as follows:1.The Nankan oil pipeline leakage had increased the primitive subsurface resisti- vity. The residual contamination plume moved from leakage source to the north or northwest direction. The contaminated area was located between eastern Nankan chi and its southwestern terrace.2.Since LNAPL was floated on the surface of groundwater, the migration of residual LNAPL was influenced by rainfall, and it can be concentrated or diluted in soil with descending and rising of groundwater level.3.In the simulation experiments, quality of measured strata resistance data by using pole-pole array or Wenner array is better than that from using self- potential. Selecting a suitable survey method for different contaminant is helpful to recognized its characters.4.The detecting systems in the experiment had good results. This indicates that the systems suggested by this research are applicable for contaminant detection. However, there still have much room to improve.

碩士<br>健行科技大學<br>空間資訊與防災研究所<br>101<br>Both leakage current method and electrical resistivity tomography were applied to investigate the testing waste landfill site to monitor the most frequently occurring leachate leakage problems. The current way for monitoring landfill leachate leakage only limited on the installation of the upstream and downstream monitoring wells. However, there is no immediate system for leachate leakage monitoring. Therefore, this study used geoelectrical methods to monitor the completeness of the high-density polyethylene (HDPE), which shows it had reach immediate monitoring and while collecting facts for follow up damage repair. In order to simulate the leakage situation in the waste landfill site we made many breakages and compared the results of both leakage current method and electrical resistivity tomography method. The leakage current method showed immediate and efficient monitoring result. By changing the interval of electrodes, the locations of breakage can be defined more exactly. The electrical resistivity tomography showed a better result by using Wenner-Schlumberger array for waste landfill sites. The results can significantly define the depth of the HDPE and the high risk areas. Combining these two methods can provide more information about the landfill leakage problems.

碩士<br>清雲科技大學<br>空間資訊與防災研究所<br>98<br>In this thesis, three case studies are used to investigate the potential application of different electrical techniques. The first case identified the existence of oil leakage of underground tanks using the electrical resistivity tomography (ERT) method. The second case located some unknown underground structures using the combination of ground penetrating radar (GPR) and ERT methods. The last case detected the illegal buried wastes using the combination of horizontal loop electromagnetic (HLEM) and ERT methods. In case one, the results show that the light non-aqueous phase liquid (LNAPL) contaminations are not only from the spilling on the surface but also from the leakage of underground tanks. In case two, the results are confirmed by post excavation after survey. In case three, the anomalous zones of HLEM and ERT are comparable. Unfortunately, there are no samplings and records of dump activities are available in the site. The results of these studies clearly demonstrate the capability of electric methods to effectively identify the existence of underground targets. Each method has its advantage and limitation, the drawback can be overcome by combination of these methods together and thereby provide necessary information for engineering work.

碩士<br>國立中央大學<br>地球物理研究所<br>100<br>The Electrode Resistivity Tomography method was used to many years. In previous studies, they compared many properties between different electrode arrays.In this study, We discuss not only resolution but also lateral effect for different electrode arrays in this study. We chose Edge-Gradient (EG) array, Pole-Dipole (PD) array, Pole-Pole (PP) array and Wenner-Schlumberger (WS) array to do the two tests. In first test, we set survey line near the buried object and then do measuring. After measuring, move survey line leave the buried object 20cm, 40cm, 60cm and 80cm respectively and then do the measuring. Finally, move survey line to 8m measure the background information in first site. In second test, we put artificial shallow conductor upon the survey line and then do measuring. After measuring, move artificial shallow conductor leave the survey line 10cm, 20cm, 30cm and 40cm respectively and then do the measuring. Finally, we remove the artificial shallow conductor to measure the background information in second site. We use resistivity image to discuss the resolution , which survey line near the target in two tests. And then discuss the lateral effect by the variation of resistivity image during moving survey or moving artificial shallow conductor. The result of resolution, Wenner-Schlumberger array and Eege-Gradient array can get better resolution images than Pole-Pole array and Pole-Dipole array. And the lateral effect of Wenner-schlumberger array is strongest in this study