2D Geoelectrical Imaging Research Articles

3D Effect and countermeasure of 2D geoelectrical imaging of a subsurface linear structure

This study was prompted by a field observation of a resistivity anomaly in a 2D Electrical Resistivity Tomography (ERT) scan during a fault investigation, suspected to be an artifact from an unnoticed 3D effect. Numerical simulations explored potential 3D effects when the survey line is not perpendicular to the strike of a linear feature, violating the ideal 2D assumption. Artifacts similar to the observed field anomaly arise when the survey line is oriented at an angle <60° from the strike. This 3D effect pattern, resulting from an oblique survey line, is quite different from the known mirroring effect of off-plane objects. Previously overlooked in practical applications, this phenomenon could lead to misinterpretations. A comprehensive investigation considering various influencing factors clarified the conditions and behaviors associated with this 3D effect. Further numerical studies of pseudo-3D surveys propose a practical guideline to avoid this effect with minimal effort. When field conditions raise concerns about surveying at an acute angle to the strike, adding one more survey line on each side of the main survey line, offset by two electrode spacings, is recommended. The 3D inversion of this narrow 3-line pseudo-3D survey can accurately resolve the in-line resistivity section.

The impact of conductive layers on depth of investigation estimation in 2D geoelectrical imaging: A case study of West Bani Mazar, El Minia, Egypt

The appearing of clay (conductive) layer(s) at different depths of the lithological succession has been widely observed in the Upper Egypt district. This phenomenon has dramatic effects on the resultant depth of investigation of any geoelectrical survey of such environment. Study the effect of such layers on estimating Depth of Investigation (DOI) is the main goal of this article. Because the reliability of the Two Dimensional Electrical Resistivity Imaging (2DERI) models alters rapidly with changing conductive layers depths as well as noisy data ratios, an accurate estimation of DOI is critical to help geophysists determining the optimum hydrogeophysical survey design in clayey environments. The modified depth of investigation method which mainly depends on the statistical method is applied to estimate the DOI. In this article, the study is based on synthetic and field data sets. Wenner (W), Wenner Schlumberger (WSC) and Dipole-Dipole (DD) electrode arrays were chosen to clarify which electrode gives larger DOI in the conceptual models (presence conductive layer at 0, 50 and 100 m depths) from the ground surface. Moreover, the study will include a test for the effect of adding 10% noise to synthetic data sets on DOI estimation.It is well known that Wenner array better matches with layer-like targets, DD with 3D horizontally limited ones. Based on these results, there is a relationship between DOI and depth of the conductive layer [larger DOI is recorded when conductive layer exists at deeper depths and vice versa].This could be related to the existence of a conductive layer in the lithology succession that can limit the current to flow vertically and subsequently, affects DOI estimation. 2D ERI field data from West Bani Mazar, El Minia is used to support the supposed first conceptual model on DOI estimation.

A Resistivity Survey of Phosphate Nodules in Oshoshun, Southwestern Nigeria

Abstract This geophysical study was carried out to determine the occurrence of phosphate nodules in the Oshoshun Formation of the Dahomey Basin, Southwestern Nigeria. The electrical resistivity method, comprising 1D vertical electrical sounding (VES; using Schlumberger array) and 2D geoelectrical imaging (using Wenner array), was used to determine the nature and depth of occurrence of the phosphate nodules. Six profile lines were established within the study area, and inverted sections were generated from the apparent resistivity data using DIPRO inversion algorithm. Five VES points were also acquired in the study area, and Win- Resist programme was used to process and interpret the field resistivity data. Four pits were dug along the profiles to verify the interpreted results. The results obtained by both techniques reveal similar geoelectric units: the top soil, clay, clayey sand and clay at different depths. These layers host pockets of phosphate nodules (78-≥651 Ωm) with varying thicknesses. The strong correlation between the lithology profiles obtained from the pits and the interpreted results of the inverted apparent resistivity sections demonstrates the efficacy of the electrical resistivity method in characterising phosphate occurrence within the formation.

2D geo-electrical imaging for groundwater exploration in Shika, along Zaria-Funtua Road north of Ahmadu Bello University main campus, Samaru, Zaria

A two dimensional (2D) geoelectrical tomography of Ahmadu Bello University Teaching Hospital Premises was carried out with the aim of identifying a suitable location for siting a borehole. This was sequel to the fact that a borehole drilled without proper geophysical investigation in the quarters for resident doctors did not produce water. State-of-the-art equipment was employed and 2D surveying proved a powerful geological mapping tool, for use in hydrogeological mapping including engineering and environmental applications. The 2D inversion results of the survey were correlated with the lithology information obtained from the boreholes in Jama’a village, and the hostels and the residential quarters of ABUTH. The stratigraphic structure of the study area is very complex and is a product of volcanic and magmatic activities of various ages. Based on the geo-electrical images obtained in the study area, three distinct layers were revealed, the overburden with an average thickness of about 16 m – 26 m. The overburden is immediately underlain by the weathered basement, 5 m – 14 m thick which consists of disintegrated schistose rock materials, sand and gravel. This layer has a relatively low resistivity due to the presence of water and clay, which reduces the permeability, so this layer is thus regarded as the aquifer. The fresh basement rock was encountered at a variable depth of between 21 m and &gt;30 m with resistivity 1223 Ωm up to 11918 Ωm. These results agree with the borehole logs. The complete set of borehole logs used in this research were obtained from the original hydro-geologic assessment report of the groundwater research department of the National Water Resources Institute (NWRI), Mando, Kaduna; Kaduna State, Nigeria.Keywords: Tomography, Inversion, Lithology, Geo-electrical, Aquifer, Borehole

2D Geo-electrical imaging for shallow depth investigation in Doon Valley Sub-Himalaya, Uttarakhand, India

A 2D geo-electric profiling was executed close to Rajpur area in Doon Valley Sub-Himalaya, Dehradun, Uttarakhand. Profiling was executed at the site Civil Services Institute (CSI) close to Morvian Institute, Rajpur Road in Dehradun for possible shallow subsurface groundwater aquifer. Two resistivity and IP profiles were carried out to discover the conceivable groundwater zones in this area. It has been discovered that there are two inimitable palaeochannels found in these areas. These two channels act an erosional channel which was before happened to be a little stream. Beneath this, there is thick gravel and coarse sand stores in the close surface which is arranged at a profundity of 0.5–5 m with a thickness of 10 m. This zone goes about as brilliant potential for shallow groundwater pockets. Besides, inside the surroundings of these rock stores, fine to medium sand is likewise present in the vast majority of the zones which also may likewise goes about as potential groundwater resources at a shallow depth. Notwithstanding, this groundwater pockets may not be adequate to address the issues of water in the mid year season and is very much prescribed to search for more profound aquifer in the study area.

Geoelectrical Exploration in South Qantara Shark Area for Supplementary Irrigation Purpose-Sinai-Egypt

This research paper is dealing with Geoelectrical Exploration as a Geophysical method used, Vertical Electrical Sounding (VES) and 2D profile imaging to find a solution of the problems affecting the research station in South of Qantara Skark. This research station is one of the desert research center stations used to develop the desert for agriculture. The area of study is suffering from the shortage of irrigation water whereas, it depends on the water flow of the tributary of Salam Canal which being not available all the time. The appropriate solutions of these problems have been delineated by the results of 1D and 2D geoelectrical measurements. It exhibits the subsurface sedimentary sequences and extension of subsurface layers in horizontal and vertical directions especially in the groundwater aquifer. Moreover, the most suitable locations of drilling water wells could be detected. The surface and subsurface layers of the quaternary deposits consists of sand, sandy clay and clay facies. Nineteen Vertical Electrical Sounding (VES) are arranged as a grid to cover the study area and two 2D geoelectrical imaging profiles are acquired. The results are represented through different contour maps and cross sections that exhibit the horizontal distribution of successive layers which reflect the lithology and changes in all directions. The water bearing layers consisted of two zones. The upper one was less salty than the lower one. The thickness of the upper zone ranges from 5 to 7 meters, but the lower zone ranges between 15 and 30 meters. The last detected layer is clay that decreases in depth towards the Southwest of the study area, causing the phenomenon of water logging. The thickness of the upper zone of the water bearing layer is inadequate for irrigation. Recommended basins to be constructed and filled through nearby drilled wells to overcome this problem. The most suitable location to dig a channel for water drainage is in the Southwest, where there is a less depth to the clay layer and all the layers are dipping toward this side