Inverse and forward numerical modeling of trishear fault‐propagation folds
Inverse and forward numerical modeling of trishear fault‐propagation folds
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DOI：
10.1029/98tc01907
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发表时间：
1998-08
期刊：
影响因子：
4.2
通讯作者：
R. Allmendinger
中科院分区：
文献类型：
--
作者：
R. Allmendinger
断层传播褶皱通常显示下盘向斜以及地层厚度的变化和其前肢的倾角，这些特征不能简单地用简单的平行扭结褶皱运动学来解释。另一种运动学模型，三剪，可以解释这些观察，以及各种其他功能，长期以来一直感兴趣的结构地质学家。直到最近，三剪才受到很少的关注，部分原因是它必须应用于数值而不是图形。开发了一个新的计算机程序来分析三剪和混合三剪-断层-弯曲褶皱变形。在构造演化过程中，通过改变三剪带的顶角和/或传播滑移比（P/S），三剪褶皱的形状可以发生很大变化。还可以对突破、背斜和向斜斜坡以及反转构造进行建模，跟踪生长地层的运动学。三剪切带内的应变可用于预测整个结构的断裂方向，通过与模拟粘土模型的比较证明了这一点。还介绍了一种通过在六参数空间（斜坡角、三剪切顶角、位移、P/S以及断层尖端线的X和Y位置）上执行网格搜索来反演最佳拟合三剪切模型的真实的结构数据的方法。通过最小二乘回归将关键层恢复到平面方位来进行反演。由于三剪提供了一个变形区的散装运动学描述，它是补充，而不是竞争，其他运动学模型。
Fault‐propagation folds commonly display footwall synclines as well as changes in stratigraphic thickness and dip on their forelimbs, features that cannot easily be explained by simple parallel kink fold kinematics. An alternative kinematic model, trishear, can explain these observations, as well as a variety of other features which have long intrigued structural geologists. Trishear has received little attention until recently, in part because it must be applied numerically rather than graphically. A new computer program has been developed to analyze trishear and hybrid trishear‐fault‐bend fold deformation. Trishear fold shape can vary considerably by changing the apical angle of the trishear zone and/or the propagation to slip ratio (P/S) during the evolution of the structure. Breakouts, anticlinal and synclinal ramps, and inversion structures can also be modeled, tracking the kinematics with growth strata. Strain within trishear zones can be used to predict fracture orientations throughout the structures as demonstrated by comparison with analog clay models. Also presented is a method for inverting data on real structures for a best fit trishear model by performing a grid search over a six‐parameter space (ramp angle, trishear apical angle, displacement, P/S, and X and Y positions of the fault tip line). The inversion is performed by restoring a key bed to a planar orientation by least squares regression. Because trishear provides a bulk kinematic description of a deforming zone, it is complementary to, rather than competing with, other kinematic models.