断层相关褶皱的三维构造几何学分析：以川西三维地震工区为例

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

现有的断层相关褶皱理论均基于平衡剖面原理而建立的二维几何学模型。所谓的假三维模型则是通过一系列的二维剖面复合而成的,真正意义上的三维断层相关褶皱理论尚未确立,仍然处于探索阶段。本文采用Trishear4.0和GoCad软件,分别构建一系列不同位移量的断层转折褶皱和三剪断层传播褶皱的二维正演剖面,将这些正演剖面按照一定的线性位移梯度平行排列,从而建立起断层转折褶皱和三剪断层传播褶皱的假三维理论模型并加以分析和讨论。进而选取川西南盆地中三维地震勘探所覆盖的邛西断层转折褶皱和盐井沟断层传播褶皱,作为真三维实际解释模型的两个实例。研究表明,邛西背斜是一个典型的剪切断层转折褶皱,盐井沟背斜是一个典型的三剪断层传播褶皱;断层相关褶皱的假三维理论模型与实际解释模型的对比分析,可以看出沿背斜走向的位移梯度是控制三维构造几何学特征的基本因素,然而自然界断层面几何学的复杂多变以及岩层力学性质的各向异性,是造成断层相关褶皱真三维理论模型难以建立的主要原因。

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.