PHYSICAL MODELING OF CREEPING-TO-LOCKED BEHAVIOR TRANSITION ALONG A STRIKE-SLIP FAULT

Physical modeling provides an opportunity to explore the formation and evolution of systems where individual parameters can be changed across different experiments. Previous experimental studies of strike-slip systems have explored a variety of parameters, such as restraining and releasing bend geometry, shear distribution, and seismic cycles.

We examine deformation in a strike-slip fault system with both creeping and locked segments. Some experiments use one material—silicone—to help visualize patterns of deformation. Other experiments use two materials: silicone below, to mimic the mid-crust, and wet kaolin on top, to mimic the upper-crust. We also vary the strain rate in the experiments in the following four ways: (1) slow creep rate (0.2 cm/s) for a relatively long period, (2) slow creep rate (0.2 cm/s) for a relatively short period, (3) fast creep rate (varied by force applied), and (4) fast creep rate (again varied by force applied) proceeded by a period of relatively slower creeping.

The average velocity fields we obtained from particle image velocimetry did not differ significantly across the different strain rate experiments. Every experiment, including silicone-only models, resulted in a zone of contraction on one side of the fault and a zone of extension on the opposite side of the fault, consistent with mechanical expectations. This suggests that the average velocity fields due to creep at a transition from creeping to locked behavior are independent of creep rate. However, the patterns of deformation within the wet kaolin layers revealed significant differences in structures that formed at varying creep rates. At slow rates, the wet kaolin behaved as a "brittle" material in accordance with rheology measurements in the clay. These physical modeling results may have implications for the development of structures within and adjacent to actively creeping faults.