Gravimetry applied to water resources and risk management in Karst areas : a case study in Parana State, Brazil
Silva Junior, Jair Silveira da & Francisco Jose Fonseca Ferreira
Parann State is located in Brazilian southern part and has an important aquifer which is the source for drinking water to a great part of the people living in Curitiba, its main city. This aquifer is a consequence of karstification phenomena and presents elements that characterize a complete karst aquifer system, like caves, underground water flow and superficial features like dolines and sinkholes. The gravity method was applied on the basis that caves and voids present a strong density contrast when compared with the surrounding rocks. The microgravity technique was employed in the surveys carried through a certain part of the referred aquifer, using in general, 5-meter spacing between observation stations. As result of the surveys, the gravity anomaly maps clearly show areas that present a considerable mass deficiency. Through the gravity inversion process, a certain body is modeled using the observed gravity data and then, the gravity effect caused by this model is calculated. Finally, the resultant model is represented graphically by a three-dimensional surface. Thus, the model allows visualizing the mass distribution in the subsurface, characterizing underground structures that may constitute the fragility of the system, identifying areas that present some geotechnical risk.
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