Document Type : Original Research Paper
Authors
1 Faculty of Mining, Petroleum & Geophysics Engineering, Shahrood University of Technology, Shahrood, Iran
2 Faculty of Mining, Petroleum & Geophysics Engineering, Shahrood University of Technology, Shahrood, Iran
Abstract
One of the main goals of geophysical methods is to image subsurface structures. Among these, electrical resistivity and electromagnetic (EM) methods are the most effective for detecting water qanats, as their responses depend on water and ion content. In this study, the electrical resistivity method was used to reveal groundwater and locate qanats through profiling surveys with the Wenner array and three electrode spacings. Two-dimensional inverse models of resistivity data clearly indicated the qanat position by low resistivity, while three-dimensional modeling further defined the qanat and its conduit. The EM34 system, a reliable frequency-domain instrument for mapping subsurface conductivity, was also applied. EM profiling perpendicular to the qanat used both vertical and horizontal dipole modes. The obtained EM models identified the qanat location through high conductivity values. In the quasi-3D EM conductivity model, only traces of the qanat appeared due to contrasts between the conductivity of soil and the qanat conduit at various depths. Results show that the EM method requires less time and personnel than resistivity surveys. However, resistivity provides higher resolution and clearer details due to shorter electrode spacing and shallower data acquisition, whereas the EM34 system collects limited information from depths shallower than one or two meters. Overall, both methods successfully detected the qanat by contrasting electrical responses—high conductivity or low resistivity—demonstrating their complementary roles in subsurface water exploration.
Keywords
- Electromagnetic (EM) methods
- EM34
- Electrical conductivity
- Electrical resistivity profiling method
- Near-surface geophysics
Main Subjects
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