Localization patterns in sandbox-scale numerical experiments above a normal fault in basement |
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| Institution: | 1. State Key Laboratory of Geomechanics and Geotechnical Engineering, Institute of Rock and Soil Mechanics, Chinese Academy of Sciences, Wuhan 430071, China;2. University of Chinese Academy of Sciences, Beijing 100049, China;3. PipeChina West East Gas Pipeline Company, Shanghai 200120, China;4. School of resources and Safety Engineering, Chongqing University, Chongqing 400044, China;5. China Academy of Safety Science & Technology, Beijing 100012, China;6. State Key Laboratory of Performance Monitoring and Protecting of Rail Transit Infrastructure, East China Jiaotong University, Nanchang 330013, China |
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| Abstract: | The finite element program ELFEN is used to study the effect of basement fault dip on the evolution of shear band patterns in unconsolidated sand. The material properties and boundary conditions of the model were chosen to correspond to generic sandbox experiments.Model results reproduce the range of structural styles found in corresponding sandbox experiments. With a basement fault dip of 60° and lower, a graben structure is formed, composed of a synthetic shear band followed by one or more antithetic shear bands. With a basement fault dip of 70° and steeper, a reverse (precursor) shear band forms first, followed by a synthetic, normal shear band that accommodates all further displacement. The dip of the synthetic shear band is close to the basement fault dip. For basement fault dips between 60° and 70°, we observe a transition in localization patterns. An analysis of the stress fields and velocity vectors in the model explains the first-order aspects of the relationships observed.We consider the observed ‘precursor-dominated’ and ‘graben-dominated’ structural domains to be important components of normal fault systems in which the first order structural style and deformation patterns are only weakly dependent on the details of the rheology of the model materials and explore the interesting problem of the change in structural style from ‘precursor-dominated’ to ‘graben-dominated’ structural domains above a normal fault in basement. We find similar structural domains in sandbox experiments for the same set of boundary conditions but with slightly different material properties, suggesting that the modeled patterns are robust within these two structural domains, (i.e. will occur over a range of similar material properties and boundary conditions).The results of this study contribute to our ability to validate numerical models against experiments in order to finally better simulate natural systems. |
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