Localising Fractures by Geoelectric Null-arrays

The term “geoelectric null-array” is used for direct current electrode configurations yielding a potential difference of zero above a homogeneous half-space. This paper presents a comparative study of the behaviour of three null-arrays, midpoint null-array (MAN), Wenner-g null-array and Schlumberger null-array in response to a fracture. The main objective is to determine which array(s) best localise vertical structures. Forward modelling of the three null-arrays revealed that the Wenner-g and Schlumberger null-arrays localise vertical fractures the most accurately. The numerical analysis served as basis to interpret the field results too. Field test measurements were carried out above a quarry in Les Breuleux (Switzerland) with the three null arrays and many classical arrays. The results were cross-validated with quarry-wall geological mapping. In real field circumstances, the Wenner-g null-array showed to be the most efficient and accurate in localising fractures. This study shows that geoelectrical null-arrays are better than classical arrays for localisation of fractures.