Imaging karst aquifers by combining deep electrical resistivity tomography with magnetic surveys, a case study of the Quchan area, NE Iran

Geophysical surveys have been carried out to characterize the structure and to better understand the karstic water reservoirs in the Quchan area. Deep 2-D resistivity tomography and magnetic method have been used to detect the most promising zones for new water-well siting.
Magnetic method has a common usage in the interpretation of the tectonic framework, faults and fractures that are triggering parameters of karstification phenomena. Therefore a high resolution magnetic survey was carried out as the first detection approach at selected sites in the studied region with the aim of probable buried fault exploration for karstic zone detection. The geomagnetic results detect magnetic anomalies in NW-SE direction agreed with the known faults system in the area. As the second approach, a Deep Electrical Resistivity Tomography (DERT) process has been designed according to magnetic results. Tree sections of 2-D electrical tomography using the Wenner-Schlumberger array has been carried out along a survey line of 100 m and an investigation depth of about 250 m with resolution of 5 m. The 2-D inversion modeling provides suitable information about the exploration targets and essential geological formations. The studies illustrate that low resistivity areas on the sections related to karstic zones. We used this combination of geophysical methods in this study to prove that these geological phenomena can be detected by such quick, economic and confident sequence of geophysical methods.