Joint use of TEM and MRS methods in a complex geological setting |
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| Authors: | Anatoly Legchenko Michael Ezersky Christian Camerlynck Abdallah Al-Zoubi Konstantinos Chalikakis |
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| Institution: | 1. Institut de recherche pour le développement (IRD-LTHE), BP 53, 38041 Grenoble cedex 9, France;2. Geophysical Institute of Israel, 6, Haba’al Shem Tov, POB 182, Lod 71100, Israel;3. UMR 7619 Sisyphe, université Pierre-et-Marie-Curie Paris 6, 4, place Jussieu, 75252 Paris cedex 05, France;4. Al-Balqa Applied University, Engineering Faculty, Salt 19117, Jordan |
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| Abstract: | Transient Electromagnetic (TEM), known also as Time Domain Electromagnetic (TDEM) and Magnetic Resonance Sounding (MRS) methods were applied jointly to investigate variations in lithology and groundwater salinity in the Nahal Hever South area (Dead Sea coast of Israel). The subsurface in this area is highly heterogeneous and composed of intercalated sand and clay layers over a salt formation, which is partly karstified. Groundwater is very saline, with a chloride concentration of 100–225 g/l. TEM is known as an efficient tool for investigating electrically conductive targets like saline water, but it is sensitive to both the salinity of groundwater and the porosity of rocks. MRS, however, is sensitive primarily to groundwater volume, but it also allows delineating of lithological variations in water-saturated formations. MRS is much less sensitive to variations in groundwater salinity in comparison with TEM. We show that MRS enables us to resolve the fundamental uncertainty in TEM interpretation caused by the equivalence between groundwater resistivity and lithology. Combining TEM and MRS, we found that the sandy Dead Sea aquifer filled with Dead Sea brine is characterized by a bulk resistivity of ρx > 0.4 Ωm, whereas zones with silt and clay in the subsurface are characterized by a bulk resistivity of ρx < 0.4 Ωm. These observations are confirmed by calibration of the TEM method performed near 18 boreholes. |
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