[1] The electrical potential field passively recorded at the ground surface of the Earth (and termed self-potential) can be analyzed to determine the shape and the depth of the piezometric surface. The coupling between hydraulic flow and electrical current density is electrokinetic in nature. The electrokinetic coupling coefficient entering into the integral equation relating the depth of the water table to self-potential signals is analyzed for various types of porous materials. It is simply related to the electrical conductivity of the pore water. In steady state conditions each element of the water table can be seen as an elementary dipole with an inclination locally perpendicular to the water table and strength proportional to the water table elevation. Then, we propose three methods to obtain the shape and range of possible depths of the water table from the study of the selfpotential distribution recorded at the ground surface. The nonuniqueness of the solution is removed if one knows either the electrokinetic coupling coefficient or the water table at one location and under the assumption of the spatial homogeneity of the electrokinetic coupling coefficient. Two field cases are discussed to show the success of the proposed methods for estimating the shape and depth of the water table at two different scales of investigations. They concern the study of self-potential signals associated with the shape of the water table in the vicinity of a pumping well and in the flank of the Kilauea volcano.INDEX TERMS: 1832 Hydrology: Groundwater transport; 5109 Physical Properties of Rocks: Magnetic and electrical properties; 5139 Physical Properties of Rocks: Transport properties; 5114 Physical Properties of Rocks: Permeability and porosity; KEYWORDS: self-potential, hydraulic charge, water table, electrokinetic, streaming potential, tomography Citation: Revil, A., V. Naudet, J. Nouzaret, and M. Pessel, Principles of electrography applied to self-potential electrokinetic sources and hydrogeological applications, Water Resour.
Les potentiels spontanés (PS) sont les potentiels électriques mesurés de façon passive à la surface de la terre. En association à d'autres méthodes géophysiques, les relevés PS sont particulièrement utiles pour localiser et quantifier les flux d'eau, les panaches de polluant, et pour estimer les propriétés hydrauliques des aquifères. Les études de laboratoire ont montré que les coefficients de couplage en jeu dépendent principalement de la composition de l'eau, sa conductivité, son pH, et de la surface du sol. L'interprétation des observations PS peut se faire qualitativement, en corrélant les gradients PS avec les flux d'eau (électrocinétique) ou avec les flux de sel (électro-diffusion). Récemment cette interprétation a été améliorée par la modélisation ou/et l'inversion de l'équation de Poisson et vise à estimer les paramètres hydrauliques en terme d'intensité de source de courant électrique induite par les flux d'eau.
In an effort to investigate the link between failure mechanisms and the geometry of fractures of compacted grains materials, a detailed statistical analysis of the surfaces of fractured Fontainebleau sandstones has been achieved. The roughness of samples of different widths W is shown to be self affine with an exponent ζ = 0.46 ± 0.05 over a range of length scales ranging from the grain size d up to an upper cut-off length ξ ≃ 0.15W . This low ζ value is in agreement with measurements on other sandstones and on sintered materials. The probability distributions π δz (δh) of the variations of height over different distances δz > d can be collapsed onto a single Gaussian distribution with a suitable normalisation and do not display multifractal features. The roughness amplitude, as characterized by the height−height correlation over fixed distances δz, does not depend on the sample width, implying that no anomalous scaling of the type reported for other materials is present. It is suggested, in agreement with recent theoretical work, to explain these results by the occurence of brittle fracture (instead of damage failure in materials displaying a higher value of ζ ≃ 0.8).
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.