New insights into the hydrogeology of a basaltic shield volcano from a comparison between self-potential and electromagnetic data: Piton de la Fournaise, Indian ocean |
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Authors: | Souad Boubekraoui Michel Courteaud Maurice Aubert Yves Albouy Jean Coudray |
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Affiliation: | aObservatoire de Physique du Globe, 12, avenue des Landais, 63000 Clermont-Ferrand, France;bLaboratoire des Sciences de la Terre, Université de la Réunion, BP 7151, 97715 Saint-Denis messag cedex 9, France;cORSTOM, Laboratoire de Géophysique, 72 route d'Aulnay, 93143 Bondy, France |
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Abstract: | In order to investigate aquifers, several geophysical surveys have been carried out in the Baril area of the southern flank of Piton de la Fournaise volcano on Reunion in the Indian Ocean using audiomagnetotelluric (AMT), very-low-frequency (VLF) and self-potential (SP) methods. We present the results with emphasis on a comparison between SP data and the findings of geoelectric surveys. AMT soundings have indicated, from the surface downward, three layers: (i) resistive volcanic rocks, (ii) an intermediate resistivity layer, and (iii) a conductive basement attributed to a seawater-bearing aquifer. VLF measurements allow the mapping of the first layer apparent resistivity, and therefore its bottom, when the true resistivity is supposed to be isotropic and homogenous. When this assumption does not hold, only the SP method permits the mapping of this bottom. Because of the good agreement between the SP and electromagnetic results, we propose the SP method as the first tool that should be used in studying shallow hydrogeological structures in volcanic areas. |
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Keywords: | Hydrogeology Self-potential method Electromagnetic method Piton de la Fournaise |
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