Mechanical behavior of non-planar faults [electronic resource] : numerical experiments and field observations

The mechanical behavior of faults and fractures is a fundamental problem for geoscientists studying deformation of Earth's brittle crust. Faults are often idealized as planar structures, although abundant evidence from geological and geophysical investigations confirm that they are geometrically complex and exhibit geometric irregularities on many scales. Faults and fractures are commonly modeled as cracks in an otherwise homogeneous and isotropic linear elastic material. Although many analytical solutions for crack problems exist, such solutions are not viable for problems where the cracks have irregular geometry or the boundary conditions cannot be prescribed. Numerical tools should then be used to solve the more computationally intensive, and more realistic, crack problems. Incorporating a complementarity algorithm into the displacement discontinuity boundary element method (DDM) merges two existing computational tools and provides an effective numerical method to investigate mechanical behavior of faults and fractures in a wide range of frictional contact problems. Complementarity is a popular optimization method used in engineering, economics, and various scientific disciplines. This dissertation investigates the mechanical behavior of faults by stepping through problems of simplified fault shapes in order to better understand the behavior of naturally non-planar faults; slip surface deformation is the focus of this work. The circular arc crack problem has served as a catalyst for testing new numerical approaches. The DDM with complementarity is employed to define when the analytical solution is not applicable and to better understand the mechanism that causes partial closure under various loading conditions by calculating the displacement discontinuities along the crack and stress intensity factors. The DDM with complementarity is also used to investigate idealized sinusoidal fault shapes. The analytical solution for an infinite sinusoidal interface does not accurately reflect important fault characteristics that influence its mechanical behavior; this necessitates use of a numerical model and precludes use of an analytical model for wavy faults. Stick, slip, and opening distributions along wavy faults with a range of uniform coefficients of friction, amplitude to wavelength ratios, and wave numbers are provided. Lastly, natural fault traces are modeled with the DDM with complementarity to demonstrate the differences between the mechanical behavior of natural fault geometries with that of the simplified planar and non-planar shapes. Meter-scale, subvertical strike-slip fault traces mapped in the Lake Edison Granodiorite in the central Sierra Nevada, California, exhibit geometric complexities which significantly contribute to their mechanical behavior. Field observations provide model geometries and parameter constraints, and new field observations provide help to elucidate slip surface deformation in this study area.

Keywords: Geological and Environmental Sciences.
Advisor: Pollard David D. primary advisor. Thesis advisor
Dunham Eric advisor. Thesis advisor
Hilley George E. advisor. Thesis advisor