Thrust formation using a numerical granular rock box experiment

A numerical granular rock box experiment based on the Discrete Element Method (DEM) was performed in thin 3D geometry to investigate the role of granularity in thrust formation. This rock box experiment is an extension of the numerical sandbox test, which is considered an analog experiment for accretionary prism formation with cohesive contact force. The parameters of contact-based interaction are adjusted to account for the failure envelope of the host rock in the triaxial test. The developed model allows the numerical simulation of the horizontal shortening of a granular layer on geologically relevant scales. The rock box test successfully reproduces the characteristic structures of accretionary wedges developed during sequential thrust formation. In contrast to the non-cohesive case, the cohesive models generated a surface geometry with steeper angles, surface vertical faults, and enhanced bifurcation of the shear bands. The geometric network of fault planes depended on the healing of the cohesive force within the faulted region. The increasing complexity of the network was demonstrated using finer elements until its maximum radius reached 12.5 m. We also evaluated the granular nature of the thrust thickness, which was found to depend on the number of frictional elements rather than physical length. A decrease in the growth rate of the fault damage zone thickness with increasing fault displacement was found to be consistent with observational data. Our results suggest an important role for granularity in thrust evolution.