Groundwater aquifer detection using the time-domain electromagnetic method: A case study in Harrat Ithnayn, northwestern Saudi Arabia

Eight time-domain electromagnetic profiles were carried out in Harrat Ithnayn, northwestern Saudi Arabia, to detect potential groundwater-bearing aquifers in the area. The collected data were processed and analyzed, with the results inferred or extrapolated between one-dimensional vertical soundings to obtain two-dimensional resistivity sections of the subsurface geological setting. We found that the resistivity values change laterally and vertically throughout the area. High resistivity values (greater than 100 Ohm-m) occupy most of the sections down to depths of approximately 100–150 m, whereas the low-resistivity regions of the section appear to be shallower than 100 m toward the west in the northern part of Harrat Ithnayn. The high-resistivity regions correspond to the Harrat basalts and are underlain by low resistivity (down to a few Ohm-m) in the saturated zones. There are also localized regions of low resistivity at depths of approximately 20–30 m, indicating shallow local groundwater aquifers. Aquifer thickness varies from approximately 50 to more than 100 m. In the southern part, the resistivity sections indicate that the main aquifer is at a depth of 150–200 m (possibly near 170 m) below the basalt. A saturated zone or shallow aquifer approximately 20–30 m thick also exists at a depth of approximately 15 m. In both the shallow and deep aquifers, the resistivity values indicate that there is good quality fresh water.