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École polytechnique de Montréal (1994)

Application de la magnétotellurique à l’étude des aquifères profonds du bassin sénégalais

Giroux, Bernard

Titre : Application de la magnétotellurique à l’étude des aquifères profonds du bassin sénégalais.

Auteur : Giroux, Bernard

Université de soutenance : École polytechnique de Montréal

Grade : M.Sc.A. 1994.

Résumé
The Magnetotelluric sounding method has been used to determine the geoelectrical and geometrical parameters of the deep Senegalese aquifer. MT was selected over other geophysical techniques for its large range of penetration which allow the imaging of deep structures under very conductive sedimentary layers. The specific goals were to verify if the MT method can resolve the top and bottom of the aquifer and the depth to the fresh water - salt water interface, together with establishing if the method can image lateral continuity of the aquifer and detect communication patterns between superposed aquifers. Interpretation of 9 MT soundings along a EW profile in Senegal showed the high potential of the method. The sedimentary portion of the basin is 1D and layered models are sufficient to describe it. Conversely, the substratum appears to be 2D and 3D and interpretation is more complex. 1D models were obtained on all of which the bottom of the aquifer and the fresh water - salt water interface are clearly visible. The top of the aquifer is not well resolved because of the weak contrast of resistivity between the late maestrichtian sands and the palaeocene calcareous. The 2D models obtained from inversion illustrate the lateral continuity of the aquifer. On the other hand, the density of the survey stations limits seriously the resolution between the stations and the possible communication zones between aquifers cannot be seen on the 2D models. The Ndiass horst and the basin subsidence are clearly visible on the 2D models. West of the 15th meridian, a regional 3D structure generates anomalous vertical fields and distortion of the impedance tensor.

Présentation (Amicus)

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