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1D single-site and laterally constrained inversion of multifrequency and multicomponent ground-based electromagnetic induction data—Application to the investigation of a near-surface clayey overburden

Abstract : Electromagnetic induction (EMI) methods are widely used to determine the distribution of the electrical conductivity and are well adapted to the delimitation of aquifers and clayey layers because the electromagnetic field is strongly perturbed by conductive media. The multicomponent EMI device that was used allowed the three components of the secondary magnetic field (the radial Hr, the tangential Hϕ, and the vertical Hz) to be measured at 10 frequencies ranging from 110 to 56 kHz in one single sounding with offsets ranging from 20 to 400 m. In a continuing endeavor to improve the reliability with which the thickness and conductivity are inverted, we focused our research on the use of components other than the vertical magnetic field Hz. Because a separate sensitivity analysis of Hr and Hz suggests that Hr is more sensitive to variations in the thickness of a near-surface conductive layer, we developed an inversion tool able to make single-sounding and laterally constrained 1D interpretation of both components jointly, associated with an adapted random search algorithm for single-sounding processing for which almost no a priori information is available. Considering the complementarity of Hr and Hz components, inversion tests of clean and noisy synthetic data showed an improvement in the definition of the thickness of a near-surface conductive layer. This inversion code was applied to the karst site of the basin of Fontaine-Sous-Préaux, near Rouen (northwest of France). Comparison with an electrical resistivity tomography tends to confirm the reliability of the interpretation from the EMI data with the developed inversion tool.
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https://hal-normandie-univ.archives-ouvertes.fr/hal-01740089
Contributor : Fayçal Rejiba <>
Submitted on : Wednesday, March 21, 2018 - 3:48:41 PM
Last modification on : Thursday, September 24, 2020 - 4:00:35 PM

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Cyril Schamper, Fayçal Rejiba, Roger Guérin. 1D single-site and laterally constrained inversion of multifrequency and multicomponent ground-based electromagnetic induction data—Application to the investigation of a near-surface clayey overburden. Geophysics, Society of Exploration Geophysicists, 2012, 77 (4), pp.WB19--WB35. ⟨10.1190/geo2011-0358.1⟩. ⟨hal-01740089⟩

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