New insights on the kinematics of fault-propagation folding from analogue models monitored using particle image velocimetry

This study aimed to understand the 2D kinematic processes associated with the development of fault-propagation folds in contractional systems. Analogue models were used to analyse the influence of, and the interplay among, various parameters, including: (1) the analogue material (quartz sand v. glass microspheres); (2) the mechanical stratigraphy (anisotropic models v. models with two different analogue-packs); and (3) the initial thickness of the analogue-pack. Each model was analysed using particle image velocimetry to quantify the spatial and temporal patterns of the strain rates during progressive deformation. The results showed that fault-propagation folding combines different kinematic mechanisms, such as flexural slip and basal thickening. Ramp initiation can occur in different ways: from the detachment, within the deformed layers or via a combination of these processes, as observed in outcrops of the Jaca–Pamplona Basin (southern Pyrenees) and the Big Bend National Park (western Texas, USA).