The Influence of Pre-existing Zones of Weakness on the 3D Geometry and Evolution of Extensional Faults and Folds

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The Earth's continental crust is heterogeneous, containing numerous pre-existing zones of weakness. How do these pre-existing zones of weakness influence the structural development of rift basins? This research project explores the hypothesis that the influence is highly variable, depending on several conditions including: 1) the attitude of the pre-existing fabric relative to the extension direction during rifting, 2) the characteristics of the pre-existing zones of weakness (i.e., their number, spacing, length), and 3) the burial depth of the pre-existing zones of weakness during rifting. To test this hypothesis, a series of scaled experimental (analog) models are run in which these three conditions vary systematically. Identical models will be conducted with dry sand and wet clay as the modeling materials to determine the sensitivity of the modeling results to the modeling medium. Additionally, the faults and fault-related folds produced in the models are compared with natural examples observed on three-dimensional seismic-reflection data from rift zones containing pre-existing zones of weakness. The integration of the results of the experimental modeling and the three-dimensional seismic analysis (data sets that yield complementary information) will provide a robust test of the hypothesis. Novel research methods include the use of thin-sections to study the details of fault interactions in clay models and the generation of three-dimensional renderings of the faults and fault-related folds produced in the experimental models using the same computer software designed for the interpretation of three-dimensional seismic-reflection data.Tectonic events have repeatedly deformed (fractured and contorted) the Earth's crust. In this project, scaled experimental models are used to study how the deformation produced during early tectonic events affects the deformation produced during subsequent tectonic events. Scaled experimental modeling is a powerful tool that has helped geoscientists understand rock deformation in three dimensions and through time. One limitation of scaled experimental modeling, however, has been the inability to observe the three-dimensional deformation in great detail. In this project, this limitation is overcome by studying the deformation in the models using thin sections (very thin slices of the model mounted on slides and viewed through a microscope) with sophisticated computer software currently used in the oil and gas industry. By combining these traditional and cutting-edge technologies, three-detailed dimensional images of the deformation within the models will be constructed, for the first time. This improved knowledge of the three-dimensional deformation patterns will have immediate applicability for earthquake prediction, ground-water flow, hydrocarbon exploration and production, and sequestration/storage of the greenhouse gas, carbon dioxide. Specifically, geoscientists will be able to use these modeling results as templates for interpreting widely spaced or poor-quality geologic or geophysical data.