Ductile creep, compaction, and rate and state dependent friction within major fault zones
Ductile creep, compaction, and rate and state dependent friction within major fault zones
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主要断层带内的延性蠕变、压实以及速率和状态相关的摩擦
DOI：
10.1029/94jb03340
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发表时间：
1995
影响因子：
--
通讯作者：
N. Sleep
中科院分区：
文献类型：
--
作者：
N. Sleep
地震期间主要走滑断层上的剪切牵引力远低于与静水压力平衡的摩擦滑动表面上的预期剪切牵引力。如果地震时的流体压力远大于静水压力，则可以解释低剪切牵引力。大多数封闭断层带内的延性蠕变压实了基质，从而增加了地震之间的流体压力。地震期间的摩擦膨胀使流体压力降低到静水压力以下，并且在地震周期中，断层带与围岩处于长期平衡状态。当岩石失去所有强度的临界孔隙率与裂缝的实际孔隙率之间的差异用作状态变量时，这种延性机制在形式上与时间相关摩擦的速率和状态理论统一。大多数破碎晶格的渗透理论证明了这种选择的合理性。与实验室中正常牵引力变化相关的时间依赖性行为可以通过形式主义来解释。数值实验中有时会出现不稳定（地震）。然而，初始摩擦蠕变期间相当少量的摩擦膨胀会降低流体压力并防止不稳定滑动。一旦不稳定发生，就会明显产生断层剪胀的两种耦合机制。 (1) 与摩擦热相关的孔隙流体的膨胀增加了流体压力，抵消了地震期间孔隙体积增加的影响。孔隙体积增加有某种趋势来平衡流体膨胀，从而使流体压力保持相对恒定。 (2) 地震期间，在断层带没有明显强化的情况下，可能会产生一些孤立的空隙，这些空隙不会立即降低整个断层带的流体压力。尽管这两个过程的程度都受到能量考虑的限制，但地震期间流体压力的变化尚未得到充分理解，无法根据可观察到的材料特性来预测应力下降。
The shear traction on major strike-slip faults during earthquakes is much lower than that expected on a frictionally sliding surface in equilibrium with hydrostatic pressure. The low shear traction is explained if the fluid pressure at the time of the earthquake is much greater than hydrostatic pressure. Ductile creep within mostly sealed fault zones compacts the matrix and thus increases fluid pressure between earthquakes. Frictional dilatancy during earthquakes decreases fluid pressure below hydrostatic, and over the earthquake cycle, the fault zone is in long-term equilibrium with the country rock. This ductile mechanism is formally unified with rate and state theory for time-dependent friction when the difference between a critical porosity where the rock loses all strength and the actual porosity of cracks is used as a state variable. This choice is justified by percolation theory of mostly broken lattices. Time-dependent behavior associated with changes in normal traction in the laboratory is explained by the formalism. Instability (earthquakes) sometimes occurs in the numerical experiments. However, fairly small amounts of frictional dilatancy during initial frictional creep decrease fluid pressure and preclude unstable sliding. Two coupled mechanisms for producing dilatancy on faults once an instability is well underway are evident. (1) Expansion of pore fluids associated with frictional heating increases fluid pressure offsetting the effects of increased pore volume during earthquakes. There is some tendency for pore volume increase to balance fluid expansion so that fluid pressure stays relatively constant. (2) Production of isolated voids that do not immediately decrease fluid pressure throughout the fault zone during earthquakes can occur to the extent that the fault zone is not significantly strengthened. Although the extent of both processes is constrained by energy considerations, the variation of fluid pressure during earthquakes is not yet well enough understood to predict stress drop from observable material properties.