Geometrical Effects of Fault Bends on Fault Stick Slip Behavior and Deformation: Insights from Distinct Element Simulations

Natural faults often consist of nonlinear segments, i.e., bends that have significant impacts on stress patterns, strain accumulation, and slip behavior of the faults. In order to study the geometrical effects of fault bends, we simulate the rupture process of faults with bends using the Distinct Element Method (DEM) in 2-D. Breakable bonds were added between particles to generate fault blocks. A nonlinear fault surface with a paired restraining bend and releasing bend was defined in between the fault blocks. Deformation was introduced by pulling a spring attached on one of the fault zone boundaries at a constant velocity while keeping the other boundary fixed. Simulations were run with a range of fault geometries, with bend angles of 0° to 40°, with varying bend height and constant bend width. All experiments demonstrated characteristic deformation involving initial smooth stick and subsequent irregular stick, in response to the transition of dominant deformation mechanism from elastic yielding of particle contacts to the development of the tensile secondary faults. This phase was followed by a slip phase accompanied by intense bond breakage and stress rotation around the restraining bend, and greater slip around the releasing bend. As geometrical effects of bends essentially result from bend enhanced frictional interlocking, higher bend angles lead to longer stick phases characterized by more significant creep, higher dilation, and greater abundance of broken bonds, and shorter slip phases are characterized by higher dilation, smaller amounts of slip, more intense fracture around the restraining bend, lower stress drops, and lower maximum slip velocities.