A methodology for converting traditional vertical electrical soundings into 2D resistivity models: Application to the Saïss basin, Morocco

Abstract

We demonstrated a simple methodology for the reinterpretation of sets of electrical vertical soundings and the production of 2D resistivity models. The method is applied to the northern central part of the subsiding Saïss basin (Morocco) where a series of vertical electrical soundings (VES) were acquired in 1982 and 1984, using the Schlumberger array with current electrodes semispacings between 3 and 3000 m. We describe a methodology used to estimate and sample apparent resistivities collected from traditional single soundings acquired by using a Schlumberger configuration. We then construct a resistivity pseudosection in a format compatible with a Wenner-Schlumberger array to perform 2D electrical tomography. The methodology takes into account the lateral and vertical spatial correlations shown by the apparent resistivities. The tomographic inversions are performed using a commercial inversion software commonly used in industry. Geostatistical tools are used to quantify the spatial correlation between apparent resistivity data. The result is a series of estimated pseudosections that are inverted to produce 2D resistivity models of the basin along geophysical profiles. We focus our attention on one of these profiles (i.e., one 2D resistivity model). The inverted geoelectrical model allows us to propose a geologic model of the basin. Our methodology allows historical and current data carried out using the Schlumberger configuration, to be rapidly reinterpreted in countries where only low-cost methods, such as VES soundings, can be used due to technology and economic constraints. It can also be applied to cases where continuous or pulled-array continuous vertical soundings method, where a tail of electrodes is towed behind a small vehicle while continuously and simultaneously measuring several electrode configurations, is inoperative due to field conditions (survey length, deep layers, and local environmental conditions).

Groundwater Exploration in Aaba Residential Area of Akure, Nigeria

“…Though applications of 2D and 3D electrical resistivity surveys to groundwater exploration and other near surface features have been reported by some authors (Aizebeokhai, 2010;Loke et al, 2013;Adagunodo et al, 2015), VES has been the most widely used configuration out of other electrical resistivity configurations, especially in the developing nations (Abudulawal et al, 2015). This is justified by its cost effectiveness, usefulness in deep subsurface mapping, and ability to image large expanse of land through geoelectrical parameters (Riss et al, 2011;Abudulawal et al, 2015). Although VES only measures resistivity variations in one-dimension, it has been found very effective in the characterization of basement geology as well as groundwater exploration (Olayinka et al, 2004;Nwankwo, 2011;Adagunodo et al, 2013b;Abudulawal et al, 2015).…”

Shallow Subsurface Stratigraphy Inferred from the Use of Vertical Electrical Soundings (VES) Survey in Central Chihuahua, Mexico

“…Since then, these electrode arrays (Wenner & Schlumberger) became very popular and are widely used in hydrogeological prospecting. The Schlumberger array offers good depth of penetration, as well as good conductive surface layer penetration, and excellent resolution of horizontal layers[28]. This array was used throughout this study because of its simpler and straightforward field logistics, and relatively quick/economic analysis using available free software (IPI2WIN).In the Schlumberger method(Figure 2), the electric current (DC or low frequency AC) is injected into the ground, between two points through 2-feet stainless-steel current electrodes (AB) driven into the ground surface, and the resulting potential difference between two other points (MN, also 2-feet stainless-steel potential electrodes) is measured.…”

Quasi-2D Resistivity Model from Inversion of Vertical Electrical Sounding (VES) Data using Guided Random Search Algorithm

“…The full 2D resistivity modeling may also be applied to VES data [17,18]. Riss, et al [19] have proposed to interpolate VES data and used 2D modeling software to interpret the data. In all cases, the non-linear inverse problems are solved by using linearization or a local search approach.…”