Fault-propagation folding occurs when a shallow fold is created by an underlying propagating thrust fault. These structures are common features of fold and thrust belts and hold key economic relevance as groundwater or hydrocarbon reservoirs. Reconstructing a fault-propagation fold is commonly done by means of the trishear model of the forelimb, a theoretical approach that assumes simplistic rheological rock properties. Here we present a series of numerical models that elucidate the kinematics of fault-propagation folding within an anisotropic sedimentary cover using complex visco-elasto-plastic rheologies. We explore the influence of different parameters like cohesion, angle of internal friction, and viscosity during folding and compare the velocity field with results from the purely kinematic trishear model. In the trishear paradigm, fault-propagation folding features a triangular shear zone ahead of the fault tip whose width is defined by the apical angle that in practice serves as a freely tunable fitting parameter. In agreement with this framework, a triangular zone of concentrated strain forms in all numerical models. We use our models to relate the apical angle to the rheological properties of the modeled sedimentary layers. In purely visco-plastic models, the geometry of the forelimb obtained can be approximated using a trishear kinematic model with high apical angles ranging between 60° and 70°. However, additionally accounting for elastic deformation produces a significant change in the geometry of the beds that require lower apical angles (25°) for trishear kinematics. We conclude that all analyzed numerical models can be represented by applying the theoretical trishear model, whereby folds involving salt layers require high apical angle values while more competent sedimentary rocks need lower values.

当下伏的扩展逆冲断层形成浅层褶皱时，就会发生断层扩展褶皱。这些结构是褶皱带和冲断带的共同特征，并且与地下水或碳氢化合物储层具有重要的经济相关性。重建断层扩展褶皱通常通过前肢的三剪模型来完成，这是一种假设简单的流变岩石特性的理论方法。在这里，我们提出了一系列数值模型，这些模型使用复杂的粘弹塑性流变学来阐明各向异性沉积盖层内断层扩展折叠的运动学。我们探索了不同参数（如内聚力、内摩擦角和折叠过程中的粘度）的影响，并将速度场与纯运动三剪模型的结果进行了比较。在 trishear 范式中，断层扩展褶皱在断层尖端前有一个三角形剪切带，其宽度由顶角定义，在实践中，顶角可作为一个可自由调节的拟合参数。与该框架一致，在所有数值模型中都形成了一个三角形集中应变区域。我们使用我们的模型将顶角与模拟沉积层的流变特性联系起来。在纯粘塑性模型中，获得的前肢几何形状可以使用具有 60° 和 70° 之间的高顶角的三剪运动模型来近似。然而，另外考虑弹性变形会导致床的几何形状发生显着变化，这需要较低的顶角 (25°) 用于三剪运动学。