Relating Slip Behavior to Off‐Fault Deformation Using Physical Models

Deformation in transform systems is accommodated by discrete fault slip and distributed off‐fault deformation. Here, we consider how a change in slip behavior along a fault can influence the distribution between on‐ and off‐fault deformation. We use a physical experiment to simplify the geometry, material properties, boundary conditions, and slip history along a strike‐slip fault to directly observe patterns of off‐fault deformation. We document deformation of a silicone slab on a simple shear apparatus using particle image velocimetry (2D) and photogrammetry (3D). The experimental results show regions of topographic highs and lows on either side of the slip transition that grow, evolve, and are displaced with progressive strain. The experimental dilatation field shares similarities with strain fields in central California along the San Andreas fault, which suggests that a change in slip behavior may explain some of the real‐world patterns in short‐ and long‐term deformation. Plain Language Summary Understanding where and why deformation occurs along a fault is important for quantifying future earthquake hazards and interpreting existing geological structures. In nature, creeping sections of strike‐slip faults move slowly and continually, while locked sections are stationary for long periods and then release large amounts of energy rapidly in earthquake events. A portion of a strike‐slip fault's total motion can be accommodated away from the main trace of the fault leading to permanent deformation. Here, we investigate how a change from locked slip to creeping slip affects deformation away from the fault trace by deforming silicone, an analog for the Earth's crust. Physical models are useful because they allow us to simplify the fault system and isolate a single variable affecting deformation. We track deformation in the experiments in two and three‐dimensions. Our results show a pattern of extension and contraction which can be compared to a real‐world change in slip behavior on the San Andreas fault. Key Points Physical models are useful for understanding where and why off‐fault deformation may occur on strike‐slip faults A change in slip behavior causes off‐fault deformation patterns to develop Experimental dilatation fields share similarities with strain fields in central California along the San Andreas fault