Transition from fault-propagation folds to fault-bend folds determined by along-strike variations of structural styles and fault displacement-distance relationships: The Sumatou anticline, Sichuan Basin, China

Abstract Understanding the evolution of thrust-related folds requires knowledge of their structural deformation over time and space, which is important for analyzing subsurface structures, hydrocarbon traps, and seismotectonic models. Here, we use high-quality 3-D seismic data interpretation and modeling to construct the subsurface structure of the Sumatou anticline in the Sichuan Basin, China. We focus on the effects of structural styles and fault displacement-distance relationships on along-strike variations in the fold deformation mechanism. Seismic interpretation reveals the along-strike variation in structural styles that formed by slip on a northwest dipping thrust fault. The fault displacement-distance profiles reveal that this structure generally follows a linear decreasing relationship, which is consistent with the pattern of fault-propagation folds (FPF). The northern segment illustrates a planar thrust ramp and self-similar growth characteristics. In contrast, the central and south segments exhibit a distinct structural style of fault-bend folding that maintains the linear decreasing trend of fault displacement-distance, which is inconsistent with fault-bend fold model (FBF) prediction. We simulate three possible fault-bending and propagating kinematic models to verify the fault displacement-distance profiles. The simulations reveal that the Sumatou anticline transitioned from early stage FPF to FBF during lateral growth. We suggest that this transition may exist in a variety of tectonic settings, such as the Sichuan Basin, the Nankai Trough, and the Niger Delta, which can be revealed by analyses of fault displacement-distance profiles and structural style variability.