Magnetotelluric soundings were carried out in the Senegal Republic on the western border of the west African craton by a team of geophysicists from Mbour's Observatory, along an approximately east–west profile. This profile includes four stations about 20 km apart. The purpose of this paper is to analyse and interpret the obtained data. The magnetotelluric data were restricted to a period range of 20–300 s. The measurements were performed individually with a reference station located in the sedimentary basin at approximately 130 km from the craton border, and they allowed one to calculate the amplitude ratios of the electromagnetic field components at the mobile stations. A two-dimensional model indicates the presence of a deep conducting layer at a depth of 80 km for the four stations. For the three stations located on the craton border the introduction of a conducting layer at a depth of 30 km permits a better approximation of the data. On the other hand, the presence of a conducting layer underneath the fourth station located on the craton is not justified by the two-dimensional model.The presence of a conducting zone in the mobile zone crust seems to have resulted from a hydration process. On the craton, the crust became hydrated and the conducting level is not present. [Journal Translation]

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