Análise da reativação de falhas normais através da modelagem física com o uso do particle image velocimetry

Abstract

Analog modeling has been used since the XIX century to simulate geological structures in order to understand the mechanisms that control their geometry and kinematics. The use of this tool in the oil industry, to help seismic interpretations (mainly searching for structural traps), helped to spread its use in the literature. Studies involving basin inversion are developed to improve understanding factors that influence the reactivation of pre-existing structures as well as their geometry. In this work, we analyze the construction of the structural architecture of a fault system that underwent positive inversion, and analyzed the relationship between the generation of new faults and reactivation of pre-existing normal faults during a contraction event. In addition, the behavior and distribution of strain along the deformation process were performed based on images obtained and processed by Particle Image Velocimetry (PIV) system. Two series of experiments were developed: i) Series I: we analyzed the generation of fault sets associated with a main listric fault and their reactivation during an inversion event. Two types of models were performed: one with listric fault, orthogonal to the direction of tension and compression (series IA), while in the other the lístrica fault was oblique (obliquity = 80) (series IB). The final structural configuration after inversion showed major fault and some of the normal faults (delimiting the grabenform structure) reactivated. Thrust and backthrust were developed from the basal portion of listric fault, or in the upper part of the model, propagating towards the base of grabenform structure; ii) Series II: we analyzed the generation of faults associated with the formation of a planar master fault, orthogonal to the direction of both tension and compression. In these experiments, the role of rheology during normal faults reactivation was analyzed. Three types of experiments were done varying the materials of the pre-tectonic sequences: sand only (series IIA); sand and gypsum ponder (series IIB); and sand and clay (series IIC). These experiments displayed the final architecture with normal faults completely or partially reactivated, and the developed thrusts and backthrust sliced up the basal portion of the grabenform structure. PIV data showed that during the first stages of compression, deformation was absorbed mainly by rearrangement of the granular material (compactation) and only after this process fault reactivation (or new fault) occurs. During deformation, some faults alternated intervals of activity and inactivity.