Detecting different water table levels in a shallow aquifer with combined P-, surface and SH-wave surveys: Insights from VP/VS or Poisson's ratios

Abstract : When applied to hydrogeology, seismic methods are generally confined to the characterisation of aquifers geometry. The joint study of pressure-(P) and shear-(S) wave velocities (V P and V S) can provide supplementary information and improve the understanding of aquifer systems. This approach is proposed here with the estimation of V P /V S ratios in a stratified aquifer system characterised by tabular layers, well-delineated thanks to electrical resistivity tomography, log and piezometer data. We carried out seismic surveys under two hydrological conditions (high and low flow regimes) to retrieve V S from both surface-wave dispersion inversion and SH-wave refraction interpretation, while V P were obtained from P-wave refraction interpretation. P-wave first arrivals provided 1D V P structures in very good agreement with the stratification and the water table level. Both V S models are similar and remain consistent with the stratification. The theoretical dispersion curves computed from both V S models present a good fit with the maxima of dispersion images, even in areas where dispersion curves could not be picked. Furthermore, V P /V S and Poisson's ratios computed with V S models obtained from both methods show a strong contrast for both flow regimes at depths consistent with the water table level, with distinct values corresponding to partially and fully saturated sediments.
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Sylvain Pasquet, Ludovic Bodet, Amine Dhemaied, Amer Mouhri, Quentin Vitale, et al.. Detecting different water table levels in a shallow aquifer with combined P-, surface and SH-wave surveys: Insights from VP/VS or Poisson's ratios. Journal of Applied Geophysics, Elsevier, 2015, 113, pp.38-50. ⟨10.1016/j.jappgeo.2014.12.005⟩. ⟨hal-01103105⟩

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