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1.
The resistivity survey for the study of subsurface hydrogeology is a continuously evolving science, which either adopts different techniques or combination of techniques to standardize the approach. The gradient profiling is done in the presence of horizontal electric field which is one of the techniques to locate the low resistivity response within the hard rock formations. This low is obtained due to presence of inhomogeneity in the host rocks. The attempt has been made to develop the concept of parallel gradient sub-profile, formulation and computation of geometrical factor, and demonstration through an actual field example in the hard rock area. The present study clearly shows that the region of low resistivity zone can easily be delineated to select a point for conducting geoelectrical sounding for knowing the information about its depth, thickness, and resistivity which are necessary requirements for ground water exploration. It can be inferred from the above study that parallel gradient sub-profile with respect to main gradient profile is useful tool for delineating low resistivity zone due to presence of fractured sandstone rocks saturated with groundwater which can be exploited.  相似文献   

2.
Zarif  Fardous  Slater  Lee  Mabrouk  Mohamed  Youssef  Ahmed  Al-Temamy  Ayman  Mousa  Salah  Farag  Karam  Robinson  Judy 《Hydrogeology Journal》2018,26(4):1169-1185

Understanding and developing groundwater resources in arid regions such as El Salloum basin, along the northwestern coast of Egypt, remains a challenging issue. One-dimensional (1D) electrical sounding (ES), two-dimensional (2D) electrical resistivity imaging (ERI), and very low frequency electromagnetic (VLF-EM) measurements were used to investigate the hydrogeological framework of El Salloum basin with the aim of determining the potential for extraction of potable water. 1D resistivity sounding models were used to delineate geoelectric sections and water-bearing layers. 2D ERI highlighted decreases in resistivity with depth, attributed to clay-rich limestone combined with seawater intrusion towards the coast. A depth of investigation (DOI) index was used to constrain the information content of the images at depths up to 100 m. The VLF-EM survey identified likely faults/fractured zones across the study area. A combined analysis of the datasets of the 1D ES, 2D ERI, and VLF-EM methods identified potential zones of groundwater, the extent of seawater intrusion, and major hydrogeological structures (fracture zones) in El Salloum basin. The equivalent geologic layers suggest that the main aquifer in the basin is the fractured chalky limestone middle Miocene) south of the coastal plain of the study area. Sites likely to provide significant volumes of potable water were identified based on relatively high resistivity and thickness of laterally extensive layers. The most promising locations for drilling productive wells are in the south and southeastern parts of the region, where the potential for potable groundwater increases substantially.

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3.
The increasing demand for freshwater has necessitated the exploration for new sources of groundwater, particularly in hard rock terrain, where groundwater is a vital source of freshwater. A fast, cost effective, and economical way of exploration is to study and analyze geophysical resistivity survey data. The present study area Omalur taluk, Salem District, Tamil Nadu, India, is overlain by Archaean crystalline metamorphic complex. The study area is a characteristic region of unconfined aquifer system. The potential for occurrence of groundwater in the study areas was classified as very good, good, moderate, and poor by interpreting the subsurface geophysical investigations, namely vertical electrical soundings, were carried out to delineate potential water-bearing zones. The studies reveal that the groundwater potential of shallow aquifers is due to weathered zone very low resistivity and very high thickness and the potential of deeper aquifers is determined by fracture zone very low resistivity and very high thickness area. By using conventional GIS method, the spatial distribution maps for different layer (top soil, weathered zone, first fracture zone, and second fracture zone) thicknesses were prepared. The geoelectrical approach was successfully applied in the study area and can be therefore easily adopted for similar environments.  相似文献   

4.
The application of electrical imaging and very low frequency (VLF) electromagnetics was investigated for the purpose of delineating basement fracture zones, and to show how incorporating a priori information in numerical modelling would facilitate the location of fractured zones within a basement rock more precisely. To this end, direct current (DC) dipole–dipole resistivity and VLF modelling and inversion experiments were carried out to evaluate the efficacy of the methods in detecting low-resistivity fracture zones in a typical crystalline basement rock that is favourable for groundwater accumulation. Most wells drilled in such an environment usually have low yields. Results of the numerical experiment generally indicate that fractures covered by moderate overburden, and having considerable depth, extent, and thickness compared to the depth of fracture burial, produce good responses resulting in high-resolution resistivity images. Lower resolution resistivity images were obtained as the thickness of the overburden increased. Also, the model investigations indicate that width of the fracture zone plays a major role in controlling image resolution. Conclusions from the synthetic modelling were confirmed by resistivity and VLF data gathered across a suspected fault in a hard rock terrain of southwestern Nigeria. The results from the field data are in general agreement with the numerical modelling experiments.Integración de métodos geofísicos superficiales para la detección de fracturas en macizos rocosos cristalinos del suroeste de Nigeria.  相似文献   

5.
As part of a larger regional research program “KarstEAU”, the authors have applied electrical resistivity tomography (ERT) techniques to characterize heterogeneities in the Port-Miou coastal karst aquifer (Cassis, SE France). Field surveys were carried out on intensely fractured and karstified Urgonian carbonates. Extensive research has characterized macro- and micro-scale geology of the Port-Miou area and particularly underground water-filled conduits and fault/fracture and karst systems within a former quarry. The authors applied 2D ERT along two surface profiles of length 420 and 595 m to test capability for delineating subsurface conduits and possibly relationship between conduit and fault/fracture/karst orientation; and 3D ERT with a dense 120 electrode array at 1 m spacing (11 × 10 m) was applied over an area of the quarry that had been profiled using 3D georadar and which has had intensive nearby structural geological interpretation. The 2D profiling imaged several underground conduits at depths to >50 m below ground surface and below sea level, including possibly the main Port Miou submarine spring and smaller springs. The 2D profiling within the quarry provided a better understanding of the connectivity between major fractures and faults on the quarry walls and secondary springs along the coast supporting flow of the secondary springs along interpreted fracture orientations. In addition, 2D inversion-derived conductivity models indicate that high resistivity zones above sea-level are associated with non-saturated zones and low resistivity anomalies in the non-saturated zone are associated with residual clays in paleokarsts. A partitioned lower resistivity zone below sea-level can be associated with a higher porosity/permeability zone with fractures and karstic features. Inversion models of the dense 3D ERT data indicate a higher resistivity volume within the larger surveyed block. The survey characterized the non-saturated zone and the ERT resistivities are correlated with karst features interpreted by 3D georadar and visible in the inferior wall of the quarry.  相似文献   

6.
 Geophysical methods, when integrated with soil chemical and hydrogeological methods, can be used to investigate groundwater contamination. Direct current (DC) resistivity geo-electrical sounding and very-low-frequency electromagnetic (VLF-EM) data were collected at an open waste site used by the municipality of the city of Isparta, Turkey. The groundwater at shallow depths in alluvium, which is composed of gravel, sand and clay, were expected to be hazardously contaminated under and around the open waste-disposal site, in which both household and industrial wastes are known to be disposed of improperly. In this study, we mapped the spread of groundwater contamination using a VLF-EM method, which allows fast and inexpensive data collection. The method complements the results of geo-electrical sounding. There is a good correlation between the results of the VLF-EM and the DC-resistivity methods employed for the investigation of subsurface structure of the site, where soil chemical and previous hydrogeological surveys have indicated high levels of chemical concentrations. Received: 17 January 2000 · Accepted: 12 August 2000  相似文献   

7.
Subsurface structures associated with hard rocks are very important for groundwater. Wadi Fatima runs through the volcanic and metamorphic rocks of the Arabian Shield which are characterized by higher magnetization than the overlaying alluvium sediments. Magnetic and direct current (DC) resistivity methods have been used for groundwater exploration in the northern part of Wadi Fatima. The magnetic survey was used mainly to map the subsurface structures, using analytic signal algorithm, of the study area. The DC resistivity method was applied to describe the lithologic domain as a function of depth, depending on their electrical property contrasts where it provided a good indication for water bearing formations. The magnetic and DC resistivity interpretations were confirmed by drilling which have provided a clear idea about the hydrogeological regime of the study area. The selected drilled well is successfully productive and it produces 30 m3/h.  相似文献   

8.
山东省蒙阴地区金伯利岩的深部地质构造特征是地学研究的热点之一。在蒙阴地区金伯利岩分布区中心部位的西峪岩带进行了10 km综合地球物理勘查,采用地震反射、大地电磁测深及重力测量解译推断出上五井和西峪两处的深部断裂构造。其中,西峪断裂带是金伯利岩浆侵入的先期控制性构造和岩浆通道,在西峪金伯利岩带内,地震反射波同相轴异常、重力低密度体、电阻率低阻异常都较为明显,且异常带有一定的连续性和规模,与已知的浅部金伯利岩体的分布形态比较吻合,推测地表延伸4 km深度内,西峪岩带内有较好的金伯利岩的发育,岩体在深部呈现节藕状间断分布。金伯利岩浆在近地表处隐爆,造成更多的破碎带和次生断裂,形成由密集零散分布的金伯利岩体组成的金伯利岩带,同时产生岩石的低电阻率和低密度异常。  相似文献   

9.
Recently, the deterioration of water quality in the coastal zones of Lekki Peninsula area of Lagos due to saltwater infiltration into the freshwater aquifer has become a major concern. With the aim of providing valuable information on the hydrogeologic system of the aquifers, the subsurface lithology and delineating the groundwater salinity, vertical electrical resistivity (VES) sounding survey was carried out utilizing surface Schlumberger electrode arrays, and electrode spacing varying between 1 and 150 m. The DC resistivity surveys revealed significant variations in subsurface resistivity. Also, the VES resistivity curves showed a dominant trend of decreasing resistivity with depth (thus increasing salinity). In general, the presence of four distinct resistivity zones were delineated viz.: the unconsolidated dry sand (A) having resistivity values ranging between 125 and 1,028 Ωm represent the first layer; the fresh water-saturated soil (zone B) having resistivity values which correspond to 32–256 Ωm is the second layer; the third layer (zone C) is interpreted as the mixing (transition) zone of fresh with brackish groundwater. The resistivity of this layer ranges from 4 to 32 Ωm; while layer four (zone D) is characterized with resistivities values generally below 4 Ωm reflecting an aquifer possibly containing brine. The rock matrix, salinity and water saturation are the major factors controlling the resistivity of the formation. Moreover, this investigation shows that saline water intrusion into the aquifers can be accurately mapped using surface DC resistivity method.  相似文献   

10.
Near-surface geophysical methods are commonly used to solve a wide class of geological, engineering and environmental problems. In this study, a geoelectrical survey was performed to investigate an alluvial aquifer. The study area is located in the southwest of the Çubukluda? graben, situated in the south of ?zmir, Turkey. The geophysical studies included the electrical resistivity imaging and self-potential (SP) methods. The resistivity data were acquired along eight profiles in the northern part of the study area by a Wenner-Schlumberger electrode configuration and the data processing was achieved by a tomographic inversion technique. The SP data were collected by gradient technique along 16 profiles. Total field values were calculated for each profile by addition of the successive gradient values, then a total field SP map was obtained. The water-saturated zone in the northern part of the study area was clearly revealed by the electrical resistivity imaging and the SP survey yielded useful information on the subsurface fluid movement.  相似文献   

11.
Geoelectrical methods involving electrical resistivity tomography (ERT), self-potential (SP), frequency domain electromagnetic (FDEM), and very low frequency (VLF) methods have been used to provide valuable information in locating a known sulfide ore body in Soap Gulch, Montana. The study develops basis of comparison for the geophysical techniques employed. Ranges of resistivity along the area have been established using interpreted ERT which can help to understand the subsurface distribution of sulfides in the area. A sulfide body was delineated from the survey area corresponding to anomalously low resistivity values on the ERT section, negative SP, and high apparent current density zone in VLF. Depth to the localized ore zone ranges approximately from 10 to 20 m. FDEM data reflect the conductivity distribution of the shallow subsurface (less than 6 m deep); hence, the delineated sulfide zone had minimal contribution to FDEM measurements. The results of the study show that SP, VLF, and ERT methods provide significant information in localizing ore bodies. The survey revealed that the resistivity values obtained from ERT profile corroborate the FDEM, SP, and VLF from the area.  相似文献   

12.
This paper presents the combination of two complementary methods, magnetic and joint inversion of resistivity/TEM data, as an effective approach to characterize groundwater reservoirs. Twenty stations of transient electromagnetic (TEM) and vertical electrical soundings (VES) were measured and interpreted using a joint inversion technique to evaluate the subsurface low resistivity zones connected to the groundwater reservoir. A complementary survey including 871 land magnetic stations was carried out at the same area to detect the upper surface of the basaltic sheet, which represents the bottom of the Miocene aquifer in the study area. The geological log from one borehole drilled in the zone was used to partially calibrate the calculated models. The results revealed that the study area consists of five different geological units with ages ranging from Paleogene (Oligocene) to Quaternary. The methodology provides good results at a very low cost when compared with drilling boreholes.  相似文献   

13.
Surface electrical and electromagnetic surveys were conducted on top of a solid waste facility in Unguwan Dosa, Kaduna State, Northwest Nigeria. The aim of the geophysical survey was to detect vertical and subvertical fractures that may provide pathways for groundwater and contaminant transport. Results from the 2D electrical resistivity imaging showed vertical and subvertical contacts overlain by 6–10 m thick overburden. Quantitative interpretation of the VLF-EM data correlates well with the results of the 2D resistivity imaging delineating the vertical and subvertical contacts as good and weak conductors (fractures zones) with resistivity values of 40–220 and 300–420 Ω m, respectively. Azimuthal Schlumberger VES measurements yield apparent anisotropy values ranging from 1.01 to 1.47 for electrode spacings of 1–45 m with the highest value recorded at spacing of 2 m. However, azimuthal variations at large spacings (30–45 m) showed no fracture anisotropy due possibly to the array’s low sensitivity to anisotropy at these spacings. The result of the study showed that pollutants in the leachate can reach and contaminate the groundwater. Therefore, urgency for leachate treatment at this site is recommended to prevent contamination of groundwater.  相似文献   

14.
An integrated study was carried out to investigate the subsurface geological conditions in a hard rock environment, with the aim of identifying zones with groundwater resource potential. The study, in Bairasagara watershed, Karnataka, India, considered geomorphology, water level, resistivity imaging, self potential, total magnetic field and susceptibility. The signatures due to lineaments have been clearly identified and their role in groundwater movement has been documented. Synthetic simulation methods were used to model the electrical response of the lineament using finite differential modeling scheme. The inverted image of the field data is compared with the synthetic image and iteration were performed on the initial model until a best match was obtained resulting on the generation of the calibrated resistivity image of the subsurface. Resistivity imaging revealed that the dykes are weathered/fractured to a depth of 6–8 m and are compact at deeper levels, and that they behave as barriers to groundwater movement, yet facilitate a good groundwater potential zone on the upgradient side. The results of magnetic surveys were utilized in differentiating granites and dolerite dykes with an insignificant resistivity contrast. Geomorphological expression alone cannot reveal the groundwater potential associated with a lineament. However, characterizing the nature of the feature at depth with integrated geophysical methods provides essential information for assessing that potential.The online version of the original article can be found at  相似文献   

15.
An integrated study was carried out to investigate the subsurface geological conditions in a hard rock environment, with the aim of identifying zones with groundwater resource potential. The study, in Bairasagara watershed, Karnataka, India, considered geomorphology, water level, resistivity imaging, self potential, total magnetic field and susceptibility. The signatures due to lineaments have been clearly identified and their role in groundwater movement has been documented. Synthetic simulation methods were used to model the electrical response of the lineament using finite differential modeling scheme. The inverted image of the field data is compared with the synthetic image and iteration were performed on the initial model until a best match was obtained resulting on the generation of the calibrated resistivity image of the subsurface. Resistivity imaging revealed that the dykes are weathered/fractured to a depth of 6–8 m and are compact at deeper levels, and that they behave as barriers to groundwater movement, yet facilitate a good groundwater potential zone on the upgradient side. The results of magnetic surveys were utilized in differentiating granites and dolerite dykes with an insignificant resistivity contrast. Geomorphological expression alone cannot reveal the groundwater potential associated with a lineament. However, characterizing the nature of the feature at depth with integrated geophysical methods provides essential information for assessing that potential.An erratum to this article can be found at  相似文献   

16.
Integrated surface electrical resistivity and electromagnetic (EM) surveys were conducted in a hard-rock terrain of Southwestern Nigeria in the vicinity of active oxidation sewage treatment ponds. The aim was to detect soil contamination due to the spread of sewage effluent, locate possible leachate plumes and conductive lithologic layers, and access the risk of groundwater pollution in the vicinity of the sewage-ponds. Dipole–dipole resistivity profiling and very low frequency (VLF) data were acquired at 10-m intervals along five 200-m long east-west geophysical traverses. Resistivity sections obtained revealed four subsurface geologic layers comprised of lateritic clay, clayey sand/sand, weathered/fractured bedrock, and competent bedrock. A distinct low resistivity zone corresponding to the contamination plume (labeled B) was delineated from all the resistivity sections. This low zone extends into the weathered bedrock and possibly suggests contamination of this layer. The filtered real component of the processed VLF data detected three distinct anomaly zones that are representative of fractured zones filled with conductive fluids and/or lithologic boundaries that possibly serve as conduits for the movement of contaminated effluents. The results obtained from the two methods suggest possible contamination of the subsurface soil layers and groundwater in the vicinity of the sewage-ponds. The existence of this contaminated plume poses a serious threat to the ecosystem and health of the people living in the vicinity of the sewage-ponds.  相似文献   

17.
A geophysical survey was undertaken at Wiri area of the Andong in southeastern Korea to delineate subsurface structure and to detect the fault zone, which affected the 1997 mountain–hill subsidence and subsequent road heaving initiated by the intense rainfall. Electrical resistivity methods of dipole–dipole array profiling and Schlumberger array sounding and seismic methods of refraction and reflection profiling were used to map a clay zone, which was regarded as the major factor for the landslide. The clay zone was identified in electrical resistivity and seismic sections as having low electrical resistivity (<100 Ωm) and low seismic velocity (<400 m/s), respectively. The clay zone detected by using geophysical methods is well correlated with its distribution from the trench and drill-core data. The results of the electrical and seismic surveys showed that slope subsidence was associated with the sliding of saturated clay along a fault plane trending NNW–SSE and dipping 10°–20° SW. However, the road heaving was caused by the slope movement of the saturated clay along a sub-vertical NNE-trending fault.  相似文献   

18.
The use of wastewater for irrigation in sandy soil increases the pollution risk of the soil and may infiltrate to the shallow groundwater aquifer. In such environment, some important parameters need to be obtained for monitoring the wastewater in the unsaturated zone over the aquifer. These parameters include clay content, heterogeneities of the upper soils, depth to the aquifer and the variations of groundwater quality. In the present work, the efficiency of DC resistivity method in forms of 1-D and 2-D measurements was studied for wastewater monitoring in the Gabal el Asfar farm, northeast of Cairo, Egypt. Forty-one Schlumberger soundings (VES) were performed then followed by three pole-dipole 2-D profiles along some considered regions within the area. The resistivity measurements were integrated with the boreholes, hydrogeological and hydrochemical (surface and groundwater samples) information to draw a clear picture for the subsurface conditions. The obtained results were presented as cross sections and 3-D visualization to trace the clay intercalations within the unsaturated zone. In addition, a vulnerability map was created using the obtained results from 1-D Schlumberger survey and confirmed with the 2-D resistivity profiling. The obtained results have shown that the 2-D resistivity imaging technique is a powerful tool for mapping the small-scale variability within the unsaturated zone and the wastewater infiltration. However, limitations of resistivity techniques were observed in the area with limited resistivity contrast such as thin clay layers with brackish water background. Under that condition, the measured pattern of resistivity distributions depends on the applied electrode array, electrode spacing and using the available geological information during the inversion process.  相似文献   

19.
Hmaima–El Gara area is located in Central–Western Tunisia and is known as an important geothermal province. In this study, we attempt to delineate the subsurface structures of the area using integrated interpretation of gravity, electrical and magnetotelluric data. The Hmaima thermal aquifer, associated with fractured Aptian reefal limestones, is characterized by high gravity and high resistivity. Horizontal gradient and Euler deconvolution method has been applied to the gravity data and provided fast information about both the depth and trends of the shallower subsurface structures in the area. As several of the mapped lineaments correlate with published geological fault trends, the other lineaments may be indicators of new insights for hydrothermal exploitation in the Hmaima–El Gara area (economical potential favorite zones).  相似文献   

20.
Electrical resistivity method is a versatile and economical technique for groundwater prospecting in different geological settings due to wide spectrum of resistivity compared to other geophysical parameters. Exploration and exploitation of groundwater, a vital and precious resource, is a challenging task in hard rock, which exhibits inherent heterogeneity. In the present study, two-dimensional Electrical Resistivity Tomography (2D-ERT) technique using two different arrays, viz., pole–dipole and pole–pole, were deployed to look into high signal strength data in a tectonically disturbed hard rock ridge region for groundwater. Four selected sites were investigated. 2D subsurface resistivity tomography data were collected using Syscal Pro Switch-10 channel system and covered a 2 km long profile in a tough terrain. The hydrogeological interpretation based on resistivity models reveal the water horizons trap within the clayey sand and weathered/fractured quartzite formations. Aquifer resistivity lies between ～3–35 and 100–200 Ωm. The results of the resistivity models decipher potential aquifer lying between 40 and 88 m depth, nevertheless, it corroborates with the static water level measurements in the area of study. The advantage of using pole–pole in conjunction with the pole–dipole array is well appreciated and proved worth which gives clear insight of the aquifer extent, variability and their dimension from shallow to deeper strata from the hydrogeological perspective in the present geological context.  相似文献   

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