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Dilatancy stabilises shear failure in rock
Earth and Planetary Science Letters ( IF 5.3 ) Pub Date : 2021-09-06 , DOI: 10.1016/j.epsl.2021.117174
Franciscus M. Aben 1 , Nicolas Brantut 1
Affiliation  

Failure and fault slip in crystalline rocks is associated with dilation. When pore fluids are present and drainage is insufficient, dilation leads to pore pressure drops, which in turn lead to strengthening of the material. We conducted laboratory rock fracture experiments with direct in-situ fluid pressure measurements which demonstrate that dynamic rupture propagation and fault slip can be stabilised (i.e., become quasi-static) by such a dilatancy strengthening effect. We also observe that, for the same effective pressures but lower pore fluid pressures, the stabilisation process may be arrested when the pore fluid pressure approaches zero and vaporises, resulting in dynamic shear failure. In case of a stable rupture, we witness continued prolonged slip after the main failure event that is the result of pore pressure recharge of the fault zone. All our observations are quantitatively explained by a spring-slider model combining slip-weakening behaviour, slip-induced dilation, and pore fluid diffusion. Using our data in an inverse problem, we estimate the key parameters controlling rupture stabilisation, fault dilation rate and fault zone storage. These estimates are used to make predictions for the pore pressure drop associated with faulting, and where in the crust we may expect dilatancy stabilisation or vaporisation during earthquakes. For intact rock and well consolidated faults, we expect strong dilatancy strengthening between 4 and 6 km depth regardless of ambient pore pressure, and at greater depths when the ambient pore pressure approaches lithostatic pressure. In the uppermost part of the crust (<4 km), we predict vaporisation of pore fluids that limits dilatancy strengthening. The depth estimates where dilatant stabilisation is most likely coincide with geothermal energy reservoirs in crystalline rock (typically between 2 and 5 km depth) and in regions where slow slip events are observed (pore pressure that approaches lithostatic pressure).



中文翻译:

剪胀作用稳定岩石中的剪切破坏

结晶岩中的破坏和断层滑动与膨胀有关。当存在孔隙流体且排水不充分时,膨胀导致孔隙压力下降,进而导致材料强化。我们使用直接原位流体压力测量进行了实验室岩石破裂实验,这表明动态破裂扩展和断层滑动可以通过这种剪胀强化效应稳定(即,变为准静态)。我们还观察到,对于相同的有效压力但较低的孔隙流体压力,当孔隙流体压力接近零并蒸发时,稳定过程可能会停止,从而导致动态剪切破坏。在稳定破裂的情况下,我们目睹了在主要破坏事件发生后持续延长的滑动,这是断层带孔隙压力补给的结果。我们所有的观察结果都由结合了滑动减弱行为、滑动引起的膨胀和孔隙流体扩散的弹簧滑块模型进行了定量解释。在反问题中使用我们的数据,我们估计控制破裂稳定性、断层扩张率和断层带存储的关键参数。这些估计值用于预测与断层相关的孔隙压力下降,以及在地震期间我们可能期望在地壳中的哪些地方出现剪胀稳定或汽化。对于完整的岩石和固结良好的断层,我们预计无论环境孔隙压力如何,在 4 到 6 公里深度之间都会有很强的剪胀强化,当环境孔隙压力接近岩石静压时,在更深的深度。在地壳的最上部(<4 km),我们预测限制剪胀性增强的孔隙流体的蒸发。在深度估计中,膨胀稳定最有可能与结晶岩(通常在 2 至 5 公里深度之间)和观察到缓慢滑动事件的区域(接近岩石静压的孔隙压力)中的地热能储层重合。

更新日期:2021-09-06
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