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Mapping Coastal Aquifers by Joint Inversion of DC and TEM Soundings-Three Case Histories |
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| Authors: | Yves Albouy Pierre Andrieux Gérard Rakotondrasoa Michel Ritz Marc Descloitres Jean-Lambert Join Eddy Rasolomanana |
| Affiliation: | 1. I.R.D., Laboratoire de Géodynamique Interne, 32 avenue Henri Varagnat, 93143 Bondy cedex, France;2. Université P. et M. Curie, Géophysique Appliquée, 4 place Jussieu, case 105, 75252 Paris Cedex 05, France;3. VAL d'OR SAGAX, 50 Boulevard Lamaque, Val d'Or, Quebec, Canada, J9P2H6;4. I.R.D., B.P. 1386 Dakar, Senegal;5. Université de La Reunion, Sciences de la Terre, 97490 Sainte-Clotilde, France;6. IOGA BP 3843 Antananarivo 101, Madagascar |
| Abstract: | Electrical and electromagnetic methods are well suited for coastal aquifer studies because of the large contrast in resistivity between fresh water-bearing and salt water-bearing formations. Interpretation models for these aquifers typically contain four layers: a highly resistive unsaturated zone; a surficial fresh water aquifer of intermediate resistivity; an underlying conductive, salt water saturated aquifer; and resistive substratum. Additional layers may be added to allow for variations in lithology within the fresh water and salt water layers. Two methods are evaluated: direct current resistivity and time domain electromagnetic soundings. Use of each method alone produces nonunique solutions for resistivities and/or thicknesses of the different layers. We show that joint inversion of vertical electric and time domain electromagnetic soundings produces a more tightly constrained interpretation model at three test sites than is produced by inversion methods applied to each data set independently. |
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