Three-dimensional structural geometry of fault-related folds: Examples from 3-D seismic explored blocks in the western Sichuan Province, China

All the current fault-related fold theories are based on the principle of balanced cross sections. The pseudo-3D model is constructed with the combination of 2D cross sections, while the true 3D fault-related fold model has not been built and is still under exploration. In this paper, we use Trishear 4.0 and GoCad programs to build a series of 2D forward cross-sections including fault-bend folds and trishear fault-propagation folds with different displacements. These sections are arrayed according to settled linear displacement gradients to construct the pseudo-3D model of fault-bend fold and trishear fault-propagation fold for our analysis and discussions. Further more, we choose the Qiongxi fault-bend fold and Yanjinggou fault-propagation fold covered by 3D seismic data as the two examples for the interpretations of the true 3D models. This research indicates that the Qiongxi anticline is a typical shear fault-bend fold and the Yanjinggou anticline a typical trishear fault-propagation fold. Through the comparison between the conceptual model and the true model, we find that the strike displacement gradients are the basic factor to control the 3D geometric features, whereas, the complexities of fault geometry and rocks mechanics anisotropy are the main difficulties to construct the true 3D conceptual model of the fault-related folds.