Resistivity imaging for identification of fracture zones in crystalline bedrock in Brazil

摘要

Geophysical methods have been extensively used in fractured rocks water prospection, with varying success levels. The objective of this article is to improve the understanding of the electrical response in 2D surveys for fractures zones mapping in crystalline rocks. 2D resistivity models simulated several types of crystalline rock fractures influenced by fracture dipping, soil coverage, and topography effects. Numerical simulations show that conceptual models are useful in evaluating the expected electrical response and planning the field survey. Field surveys were conducted on areas where fractures and faults are known from geological mapping and groundwater wells: crystalline gneissic bedrock (Louveira), diabase sill from Serra Geral Formation (Tiete), and basalt from Serra Geral formation with sediments coverage (Bebedouro). Fractures and faults were identified by resistivity values lower than 250 Ω m, confirmed by well drilling.