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首页> 外文期刊>Journal of Geophysical Research. Biogeosciences >Testing constitutive equations for brittle-ductile deformation associated with faulting in granitic rock
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Testing constitutive equations for brittle-ductile deformation associated with faulting in granitic rock

机译：试验脆性岩体断层相关的脆性延展变形的组成方程

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Uncertainty in constitutive equations for brittle-ductile deformation limits our understanding of earthquake nucleation and propagation at the base of the seismogenic lithosphere. To reduce this uncertainty, we investigate exhumed strike-slip faults and related deformation features in the Lake Edison granodiorite (central Sierra Nevada, CA) that developed at 250-500 degrees C and similar to 250 MPa. The Seven Gables outcrop contains a 10 cm wide contractional fault step separating 2 m-scale left-lateral faults. Within the step, an similar to 4 cm thick leucocratic dike is stretched and rotated, thus constraining the kinematics of deformation, and the dike and surrounding granodiorite are strongly mylonitized. Petrographic and electron backscatter diffraction analyses reveal evidence for brittle and plastic deformation mechanisms, including dislocation creep, diffusion creep, microfracturing, and cataclasis. We present a 2-D finite element model of the Seven Gables outcrop that tests a series of candidate constitutive equations: Von Mises elastoplasticity, Drucker-Prager elastoplasticity, power law creep viscoelasticity, two-layer elastoviscoplasticity, and coupled elastoviscoplasticity. Models based on Von Mises yielding most accurately match the outcrop deformation. Frictional plastic yield criteria (i.e., Drucker-Prager) are incapable of reproducing the outcrop deformation due to the elevated mean compressive stress and reduced plastic yielding within the model fault step. Furthermore, the power law creep viscoelastic model requires a high strain rate (similar to 10(-4)s(-1)) to resolve slip on faults and fails to localize strain within the step region. Comparing model results and elastic stress fields with field observations suggests that deformation localizes in regions of elevated mean compressive stress and Mises equivalent stress.
机译：脆性韧性变形的本构方程中的不确定性限制了我们对地震岩石基地地震成核和繁殖的理解。为了减少这种不确定性，我们调查了在250-500摄氏度和类似于250 MPa的湖Edison Granodiorite（Central Sierra Nevada，CA）中挖掘出挖掘的防滑故障和相关变形特征。七个Gables露出10厘米宽的合同故障步骤，分离2 M级左侧故障。在该步骤中，类似于4厘米厚的人民堤，拉伸和旋转，从而限制变形的运动学，堤防和周围的Granodiorite强烈毫透明。岩体和电子反向散射衍射分析揭示了脆性和塑性变形机制的证据，包括位错蠕变，扩散蠕变，微粘接和催化剂。我们展示了七个Gables露头的二维有限元模型，测试了一系列候选本构方程：von Mises弹性塑料，滴漏弹塑性，动力法蠕变粘弹性，双层弹性觉起来和耦合的弹性缺口性。基于VON MISES的模型产生最精确地匹配露头变形。摩擦塑料屈服标准（即，Drucker-PRAGer）不能再现由于升高的平均压缩应力和模型故障步骤内的塑料减少而导致的膨胀变形。此外，电力法蠕变粘弹性模型需要高应变速率（类似于10（-4）S（-1）），以解决故障的滑移并且未能在步进区域内定位应变。比较模型结果和具有现场观测的弹性应力场表明，变形在升高的平均压缩应力区域中定位在升高的抗压应力和误报等效应力中。

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