Influence of Shear Heating and Thermomechanical Coupling on Earthquake Sequences and the Brittle‐Ductile Transition
Influence of Shear Heating and Thermomechanical Coupling on Earthquake Sequences and the Brittle‐Ductile Transition
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DOI：
10.1029/2020jb021394
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发表时间：
2021-05
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影响因子：
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通讯作者：
K. Allison;E. Dunham
中科院分区：
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作者：
K. Allison;E. Dunham
大陆地壳断层上的局部摩擦滑动在深部转变为粘性剪切带中的分布变形。这种脆-韧性转变（BDT）和/或从速度弱化（VW）到速度强化（VS）摩擦的转变受岩石圈热结构和成分的控制。在这里，我们调查这些转变，以及它们对地震深度范围的影响，使用2D反平面剪切模拟与速率和状态摩擦的走滑断层。断层外材料是粘弹性的，具有温度依赖的位错蠕变。我们求解温度的热方程，考虑摩擦和粘性剪切加热，这种加热会产生相对于环境地热的热异常，从而降低粘度并促进粘性流动。我们探讨了几个地热和有效的正应力分布（通过改变孔隙压力），量化的热异常，地震和地震滑动，从摩擦滑动到粘性流动的过渡。在具有静水压力的模型中，热异常可以达到孕震区以下几百度，但是对于更高的压力，热异常更小（并且这些高压模型与圣安德烈亚斯断层热流约束最一致）。剪切加热提高了BDT，有时它限制了破裂深度，而不是摩擦VW到VS的转变。我们的热力学模型框架可用于评估岩石圈流变学和热模型，通过预测地震破裂，震后和震间地壳变形，热流和地质结构，反映了断层下的复杂变形。
Localized frictional sliding on faults in the continental crust transitions at depth to distributed deformation in viscous shear zones. This brittle‐ductile transition (BDT), and/or the transition from velocity‐weakening (VW) to velocity‐strengthening (VS) friction, are controlled by the lithospheric thermal structure and composition. Here, we investigate these transitions, and their effect on the depth extent of earthquakes, using 2D antiplane shear simulations of a strike‐slip fault with rate‐and‐state friction. The off‐fault material is viscoelastic, with temperature‐dependent dislocation creep. We solve the heat equation for temperature, accounting for frictional and viscous shear heating that creates a thermal anomaly relative to the ambient geotherm which reduces viscosity and facilitates viscous flow. We explore several geotherms and effective normal stress distributions (by changing pore pressure), quantifying the thermal anomaly, seismic and aseismic slip, and the transition from frictional sliding to viscous flow. The thermal anomaly can reach several hundred degrees below the seismogenic zone in models with hydrostatic pressure but is smaller for higher pressure (and these high‐pressure models are most consistent with San Andreas Fault heat flow constraints). Shear heating raises the BDT, sometimes to where it limits rupture depth rather than the frictional VW‐to‐VS transition. Our thermomechanical modeling framework can be used to evaluate lithospheric rheology and thermal models through predictions of earthquake ruptures, postseismic and interseismic crustal deformation, heat flow, and the geological structures that reflect the complex deformation beneath faults.