Event succession and geometry of the central part of the Villa de Reyes aquifer (San Luis Potosí, Mexico) inferred from geoelectric data
The geometry of the aquifer of the Villa de Reyes graben (San Luis Potosí, México) was inferred from the study of the underground electric properties in the La Pila – Jesús María region. The results of 104 vertical electrical soundings (VES) were used to establish two georesistivity trends with N-S and NE-SW directions. The N-S trend is related to the San Luis Potosí graben and the NE-SW trend to the Villa de Reyes graben. The basement of the continental basins in these tectonic depressions is formed by volcanic rocks with resistivities (ρ) between 67 and >500 Ωm. The lower values are interpreted as fractured rocks containing water, and the higher values as dry, unfractured basement. The San Luis Potosí and Villa de Reyes grabens are partially filled by upper Cenozoic continental sediments. Coarse-grained sediments, such as gravel and sand deposits, predominate in the southern portion of the studied area. These sediments have ρ values in the order of 21 to 35 Ωm. In the northern part of the area, the coarsest deposits are restricted to the borders of the basin and the fine-grained sediments –such as silt and clay, with ρ values of 10 to21 Ωm– predominate toward the central part. Three geoelectric pseudosections were prepared using apparent resistivity (ρa) values derived from the VES. On the basis of these pseudosections, a buried horst, probably related to the Villa de Reyes fault system, is inferred near the western border of the valley. The data derived from the pseudosections are also used to speculate about the tectonic events that led to the formation of the valley. It is proposed that the N-S trending San Luis Potosí graben is older and was partially overprinted in the area by the NE-SW trending faults of the Villa de Reyes graben.
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