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Exploring Long-term Fault Evolution in Obliquely Loaded Systems Using Tabletop Experiments and Digital Image Correlation Techniques
This thesis focuses on the use of scaled physical experiments to better understand the development and long-term evolution of fault systems that are otherwise impossible to observe directly. The document is divided into three chapters. The first chapter documents the implementation of an inexpensive stereo vision method for acquiring high resolution three-dimensional strain data for table-top experiments. The second chapter applies the stereo vision method to a tectonic problem—the development of slip partitioning in obliquely loaded crustal systems. Slip partitioned fault systems accommodate oblique convergence with different slip rake on two or more faults and are well documented in the crust. In this chapter, we simulate oblique convergence using blocks with 30° dipping contacts under wet kaolin clay. The experiments reveal three styles of slip partitioning development—contingent upon convergence angle and the presence or absence of a pre-existing vertical fault. Across all experiments, the slip rates along slip-partitioned faults vary temporally suggesting that the faults continuously adjust to conditions produced by the other fault. The lack of steady state in the experiments suggests that slip-partitioned crustal systems may also evolve with oscillating behavior rather than developing a single efficient active fault structure to accommodate oblique convergence. The third chapter documents rheological tests of wet kaolin for applications to crustal deformation experiments. This chapter investigates thixotropy in the clay as well as the role of grain size distribution and water content on its shear strength
Stereovision Combined With Particle Tracking Velocimetry Reveals Advection and Uplift Within a Restraining Bend Simulating the Denali Fault
Scaled physical experiments allow us to directly observe deformational processes that take place on time and length scales that are impossible to observe in the Earth’s crust. Successful evaluation of advection and uplift of material within a restraining bend along a strike-slip fault zone depends on capturing the evolution of strain in three dimensions. Consequently, we require deformation within the horizontal plane as well as vertical motions. While 3D digital image correlation systems can provide this information, their high costs have prompted us to develop techniques that require only two DSLR cameras and a few Matlab® toolboxes, which are available to researchers at many institutions. Matlab® plug-ins can perform particle image velocimetry (PIV), a technique used in many analog modeling studies to map the incremental displacements fields. For tracking material advection throughout experiments more suitable Matlab® plug-ins perform particle tracking velocimetry (PTV), which tracks the complete two-dimensional displacement path of individual particles. To capture uplift the Matlab®Computer Vision ToolboxTM, uses pairs of photos to capture the evolving topography of the experiment. The stereovision approach eliminates the need to stop the experiment to perform 3D laser scans, which can be problematic when working with materials that have time dependent rheology. We demonstrate how the combination of PIV, PTV, and stereovision analysis of experiments that simulate the Mount McKinley restraining bend reveal the evolution of the fault system and three-dimensional advection of material through the bend