Misinterpretation caused by 3D effects on 2D Electrical Resistivity Tomography: tests on simple models

The aim of this work is to evaluate the effects of 2D inversion of electrical resistivity data when in presence on 3D structures by testing synthetic and experimental models. Several numerical simulations have been calculated for different resistivity models and 2D datasets were extracted to study and quantify the effects of 2D inversion on 3D structures. Results have been compared with field texts carried out in quarrying sites. The main tests here presented simulates prism-shaped cavities with a square vertical section of l x l size and a variable lateral extension d, from l to infinity (this latter being a 2D tunnel model). Inversion of predicted data show that 2D tomography does not always give satisfactory results on cavities that have a more or less limited extension perpendicular to the profile. In all cases the resistivity anomaly obtained by the 2D inversion of a 3D cavity underestimates the true value much more than the inversion of the corresponding 2D model and obviously underestimation increases with three-dimensional characteristics. The effects of three-dimensionality can lead to the identification of false cavities along the vertical or can lead to strong errors in the estimation of depth and size, thus causing misleading statements.