Corrections of Surface Fissure Effect on Apparent Resistivity Seasurements

gance, j. ; sailhac, p. ; malet, j.-p.;

Electrical resistivity tomography (ERT) is a useful tool to detect and track water flow paths in the subsoil. However, measurements are strongly affected by sub surface heterogeneities such as fissures of different sizes and genesis (shrinking-swelling, macropores and deformation). In this work, we focus on surface fissures characterized by dimensions lower than the interelectrode spacing and correct their effect on apparent resistivity pseudo-sections by incorporating fissure geometry in the topography. We show that fissures with depths greater than 0.10 times the interelectrode spacing for a dipole–dipole array and equal to 0.16 for the gradient array and the Wenner–Schlumberger arrays create significant anomalies (greater than 5percent) in the pseudo-section. Surface fissure widths and dip angles have little effect with respect to the fissure depths which can increase the apparent resistivity up to 200percent. The clogging of thefissureswithwaterorsoilmaterialdecreasestheanomalyeffectlinearlywiththepercentage of filling. The correction of apparent resistivity values is possible for relatively simple fissure geometries and only requires a manual survey of the surface fissures. It allows to improve the quality of the inverted resistivity section by mitigating the inversion artefacts and therefore a better interpretation.