THE EVOLVING STRUCTURAL COMPLEXITY OF RESTRAINING BENDS IMPACTS SLIP RATE

Crustal restraining bends along strike-slip faults exhibit a range of structural complexities, such as number and connectivity of active faults. The evolving structural complexity of the fault system may impact slip rates at sites along restraining bends as faults within the system grow, connect, and die. For example, complex restraining bends with larger number of fault connections may have greater slip rate variations at individual sites along fault segments. Analog models allow us to directly observe and document faulting and slip rate histories that are complete through both time and space. To test the impact of initial bend geometry on evolving structural complexity and slip rate, we run and analyze analog models of restraining bends with angles of 15° and 30°. We use wet kaolin as an analog material for the crust because it produces long-lived and sharp faults that can reactivate. Greater number of active faults grow and connect to nearby faults at the surface in the 30° experiment than in the 15° experiment. In both models, the kinematic efficiency of the system, which is the ratio of deformation accommodated as slip on faults to the applied displacement, varies with the growth, linkage, and death of some faults. However, the variations in the overall kinematic efficiency do not reliably represent slip rate variations at individual sites along faults. The 30° restraining bend experiment produces greater slip rate variations at individual sites than the 15° experiment because the 30˚ experiment develops a greater number of concurrently active and connected faults. The slip rate at sites along several fault segments can vary by up to 40% when one fault either connects to or disconnects from a nearby fault. The variability of slip rates at sites along restraining bends depends on the evolution of structural complexity and specifically, the evolving connectivity of the fault system. Restraining bend systems that have a greater number of concurrently active faults and higher fault connectivity produce greater slip rate variations at sites along the faults. This suggests that slip rate records at sites along complex restraining bends may not reliably estimate the future slip rates.