Dilatancy stabilises shear failure in rock
Dilatancy stabilises shear failure in rock
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DOI：
10.1016/j.epsl.2021.117174
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发表时间：
2021-09-06
影响因子：
5.3
通讯作者：
Brantut, Nicolas
中科院分区：
文献类型：
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作者：
Aben, Franciscus M.;Brantut, Nicolas
结晶岩中的破裂和断层滑动与扩容有关。当存在孔隙流体且排水不畅时，扩容会导致孔隙压力下降，进而使材料强度增加。我们进行了实验室岩石破裂实验，并直接在原位测量流体压力，结果表明，这种扩容强化效应可使动态破裂传播和断层滑动稳定下来（即变为准静态）。我们还观察到，在相同有效压力但孔隙流体压力较低的情况下，当孔隙流体压力接近零并汽化时，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，我们观察到在主要破坏事件之后由于断层带孔隙压力重新补充而持续长时间的滑动。我们所有的观察结果都可以通过一个结合了滑动弱化行为、滑动诱导扩容和孔隙流体扩散的弹簧 - 滑块模型进行定量解释。通过反问题利用我们的数据，我们估算了控制破裂稳定、断层扩容速率和断层带储存的关键参数。这些估算值被用于预测与断层活动相关的孔隙压力下降，以及在地壳的哪些位置我们可能预期在地震期间会出现扩容稳定或汽化现象。对于完整岩石和胶结良好的断层，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强烈的扩容强化，并且当环境孔隙压力接近静岩压力时，在更深的深度也会如此。在地壳最上部（<4公里），我们预测孔隙流体会汽化，这限制了扩容强化。最有可能出现扩容稳定的深度估计与结晶岩中的地热能储层（通常在2到5公里深度之间）以及观察到慢滑事件的区域（孔隙压力接近静岩压力）相吻合。(c) 2021作者。由爱思唯尔出版公司出版。
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 (< 4km), 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). (c) 2021 The Author(s). Published by Elsevier B.V.