It has been assumed that the orientation of the maximum horizontal compressive stress (S_Hmax) in the upper crust is governed on a regional scale by the same forces that drive plate motion. However, several regions are identified where stress orientation deviates from the expected orientation due to plate boundary forces (first-order stress sources), or the plate wide pattern. In some of these regions, a gradual rotation of the S_Hmax orientation has been observed.Several second- and third-order stress sources have been identified in the past, which may explain stress rotation in the upper crust. For example, lateral heterogeneities in the crust, such as density and petrophysical properties, and discontinuities, such as faults, are identified as potential candidates to cause lateral stress rotations. To investigate several of these candidates, generic geomechanical numerical models are set up with up to five different units, oriented by an angle of 60^∘ to the direction of shortening. These units have variable (elastic) material properties, such as Young's modulus, Poisson's ratio and density. In addition, the units can be separated by contact surfaces that allow them to slide along these vertical faults, depending on a chosen coefficient of friction.The model results indicate that a density contrast or the variation of Poisson's ratio alone hardly rotates the horizontal stress (≦17^∘). Conversely, a contrast of Young's modulus allows significant stress rotations of up to 78^∘, even beyond the vicinity of the material transition (>10 km). Stress rotation clearly decreases for the same stiffness contrast, when the units are separated by low-friction discontinuities (only 19^∘ in contrast to 78^∘). Low-friction discontinuities in homogeneous models do not change the stress pattern at all away from the fault (>10 km); the stress pattern is nearly identical to a model without any active faults. This indicates that material contrasts are capable of producing significant stress rotation for larger areas in the crust. Active faults that separate such material contrasts have the opposite effect – they tend to compensate for stress rotations.

中文翻译：

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应力旋转——岩石刚度和断层的影响和相互作用

已经假设上地壳中最大水平压缩应力 ( S _Hmax ) 的方向在区域尺度上由驱动板块运动的相同力控制。然而，由于板边界力（一阶应力源）或板宽模式，确定了几个应力方向偏离预期方向的区域。在其中一些区域，S _Hmax的逐渐旋转 方向已经被观察到。过去已经确定了几个二阶和三阶应力源，这可以解释上地壳的应力旋转。例如，地壳中的横向非均质性（例如密度和岩石物理特性）和不连续性（例如断层）被确定为导致横向应力旋转的潜在候选对象。为了研究这些候选中的几个，通用地质力学数值模型设置了多达五个不同的单元，以 60 ^∘的角度定向缩短的方向。这些单位具有可变（弹性）材料属性，例如杨氏模量、泊松比和密度。此外，根据选定的摩擦系数，单元可以通过允许它们沿着这些垂直断层滑动的接触面分开。模型结果表明，单独的密度对比或泊松比的变化几乎不会旋转水平应力（≤ 17 ^∘ )。相反，杨氏模量的对比允许高达 78 ^{∘ 的}显着应力旋转，甚至超出材料过渡附近（> 10  km）。当单元被低摩擦不连续性（只有 19 ^∘与 78 ^∘）分开时，对于相同的刚度对比，应力旋转明显减少。均质模型中的低摩擦不连续性在远离断层（>10 公里）时根本不会改变应力模式；应力模式几乎与没有任何活动断层的模型相同。这表明材料对比能够对地壳中较大的区域产生显着的应力旋转。分离这种物质对比的活动断层具有相反的效果——它们倾向于补偿应力旋转。