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ABSTRACT. Areas with geological substrate composed of carbonate rocks, such as some areas of hydrocarbons exploration and production, occasionally may be related to cases of subsidence of the surface, sometimes caused by the instability of the areas associated with zones of dissolution and its voids, which commonly evolve from systems of pre-existing fractures. The physical infrastructure of these areas (buildings, oil storage tanks and waste materials, and others) can be compromised, affecting, in turn, the integrity of the geological substrate from an environmental point of view. This context includes the epigenetic karst, associated with the percolation of rainwater, focus of this work. Thus, the use of geophysical methods (notably the resistivity) allows to analyze satisfactorily, in terms of resolution and depth of investigation, the carbonate substrate and their areas of dissolution. Therefore, this research shows initially a modelling phase of several hypothetical karst systems, for the purpose of compare the different responses of the arrays used (Schlumberger, Dipole-Dipole and Wenner), followed by a qualitative analysis of real data collected in the field, which were used as a basis for defining the values of geoelectric models, from an interactive analysis. In this phase of forward modeling, synthetic geoelectrical models were generated in order to simulate an approximate geology characterized by karstic features and its geoelectric response. The inversion process aimed at validating the geophysical responses obtained from the initial models and, thus, eliminate any distortions observed in the pseudo-sections of apparent resistivity, adjusting the values of the electrical resistivity to values near the initial model proposed. Finally, the data initially modeled were corroborated by the real data. Keywords: karst, geoelectrical, modeling, environment, geotechnics. RESUMO. Regiões que apresentam substrato geológico composto por rochas carbonáticas, a exemplo de algumas áreas de exploração e produção de hidrocarbonetos, podem estar associadas a casos de abatimento da superfície do terreno, provocados ocasionalmente pela instabilidade das áreas relacionadas a zonas de dissolução e seus vazios, os quais, por sua vez, comumente evoluem a partir de sistemas de fraturas pré-existentes. A infraestrutura física destas áreas (edificações, tanques de armazenamento de petróleo e seus resíduos, entre outras) pode ser comprometida, afetando a integridade do substrato geológico do ponto de vista ambiental. Este contexto engloba o carste epigenético, associado à percolação de águas meteóricas, foco do presente trabalho. Deste modo, o uso de métodos geofísicos (notadamente a eletrorresistividade) permite analisar de maneira satisfatória, quanto aos aspectos de resolução e profundidade de investigação, o substrato carbonático e as respectivas zonas de dissolução. Para tanto, este trabalho de pesquisa trata inicialmente de uma fase de modelagem de diversos sistemas cársticos hipotéticos, de modo a comparar as diferentes respostas dos arranjos utilizados (Schlumberger, Dipolo-Dipolo e Wenner), seguida da análise qualitativa de dados reais coletados em campo, os quais foram utilizados como base para a definição dos valores dos modelos geoelétricos, a partir de uma análise interativa. Nesta etapa de modelagem direta foram gerados modelos geoelétricos sintéticos, a fim de simular de forma aproximada uma geologia caracterizada por feições cársticas e sua resposta geoelétrica. O processo de inversão nos dados obtidos pela etapa da modelagem buscou validar as respostas geofísicas obtidas a partir dos modelos iniciais e assim eliminar as eventuais distorções observadas nas pseudo-seções de resistividade aparente, ajustando os valores de resistividade elétrica a valores próximos do modelo inicial proposto. Por fim, os dados modelados inicialmente foram corroborados pelos dados reais. Palavras-chave: carste, geoelétrico, modelagem, meio ambiente, geotecnia.

The traditional methods to locate water wells in crystalline terranes are being re-evaluated aiming to improve the success rate of the procedures. We describe the preliminary approach being used in the eastern crystalline domain of Rio Grande do Norte (NE Brazil), encompassing areas around Santo Antônio and Santa Cruz cities. Emphasis is given to re-evaluate the classical structural criteria in the light of modern concepts on rock deformation and the regional tectonic framework, especially in the context of the neotectonic stress regime. At a first step, the structural analysis is applied to better understand the formation and/or reactivation of brittle structures, their chronology, and past and present kinematics. Then, these informations are used to understand water flow and accumulation in fracture aquifers, and the reasons for success or failure in the location of water wells already drilled in the region, in the hope to establish a more consistent and practical routine methods. Lineament maps of the studied areas were generated to determine the main fracture sets for well location. Structural data were collected near selected water wells, locally combined with geophysical data. Neotectonic reactivation is evaluated both from regional and local information, as available. In some cases, as in Tararaca Farm near Santo Antônio, a correlation was found between a fracture zone and a photointerpreted lineament following a drainage; the favorable orientation of the fractures, at a high angle to the present (neotectonic) extension direction, appears to convey an important control in water accumulation and well production. In other cases, as in the Santa Rita Farm near Santa Cruz, the photolineament and the drainage do not correspond to a fracture zone; and the accumulation of water is related to the opening of foliation surfaces by weathering, its intersection with different fracture sets and favorable recharge conditions provided by locally thicker, alluvial covers, forming a through-like structure.