Polygonal fault systems are geologic structures found within fine-grained sedimentary rocks and have been documented globally in submarine sedimentary basins, including the North Sea, the Denver Basin, and the South China Sea. These faults are characterized by layer-bound, multi-directional normal faults oriented in polygonal patterns in plan view and are typically confined to mudstone-dominated sedimentary sequences deposited under low regional tectonic strain (Watterson et al., 2000). Although multiple hypotheses have been proposed to explain the formation of polygonal fault systems, their widespread occurrence in submarine basins suggests that volumetric contraction associated with sediment compaction or dewatering is a fundamental and common process in sedimentary rocks deposited within marine environments.

If volume loss is common in relatively undeformed sedimentary basins, it is likely that similar processes operate in sedimentary basins that experience tectonic shortening, such as submarine foreland basins and accretionary prisms. In these settings, volumetric contraction may influence structural geometries, fault and fracture spacing, and strain partitioning within deformed sedimentary wedges. However, many structures observed in deformed sedimentary basins are commonly attributed solely to large-scale tectonic stresses, potentially obscuring the role of internal volume loss. Physical analog modeling offers a means to isolate the structural effects of volume loss by comparing deformation in experiments with and without volumetric contraction, allowing for the identification and comparison of structures that require volume loss to form versus those that form under purely shortening strain.

To investigate these processes, we conducted a series of analog deformation experiments using a physical model designed to simulate volume loss in deforming sediments. The model employs clay-rich material that undergoes volumetric contraction through drying, producing polygonal fracture patterns like natural polygonal faults. This material is deformed within the analog modeling apparatus by pulling it against a rigid backstop.  Deformation is driven by a 100:1 geared stepper motor capable of extremely low strain rates, enabling experiments to run faster than, slower than, and at rates comparable to clay volume-loss velocities. Volume-loss rates were calculated using time-lapse photography of drying clay.