Fluid driven shear cracks on a strengthening rate-and-state frictional fault
Fluid driven shear cracks on a strengthening rate-and-state frictional fault
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DOI：
10.1016/j.jmps.2019.07.015
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发表时间：
2019-11-01
影响因子：
5.3
通讯作者：
Dublanchet, P.
中科院分区：
文献类型：
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作者：
Dublanchet, P.
这项研究致力于研究流体注入刺激断层上缓慢滑移（或蠕变）重新激活的动力学。流体驱动的慢滑移事件涉及滑移率太小而无法产生可检测的弹性波（通常小于 1 cm.s(-1)），通常在构造活动区域或深层能源开发框架中的自然断层上观察到。我们将断层建模为嵌入弹性介质中的平面二维速度强化速率和状态摩擦界面。流体以恒定速率注入并沿断层扩散，减少有效正应力。我们表明，流体注入在断层上引发了剪切裂纹。在第一阶段，剪切裂纹仍然局限于加压区域，并且滑移率随时间呈指数增加。第二阶段在裂纹快速扩展开始时开始。第二阶段的剪切裂纹比加压区扩展得更快。根据预应力条件，剪切裂纹会演化为两种不同的状态。如果初始剪切应力 ro 大于裂纹内的稳态残余摩擦应力 tau(r)，则滑移速率和裂纹扩展速率会在有限时间内爆炸。这种加速裂纹状态类似于断层上动态破裂的成核。另一方面，如果 tau(0) < tau(r)，则加速扩展逐渐减慢，使得裂纹进入稳定状态，其特征是恒定的扩展速度和滑移率的对数增加。然而，绝大多数断层情景最终都会导致这种稳定的扩张状态，这也是真实构造断层上最有可能出现的情况。除了数值结果之外，我们还开发了断层上最大滑动速率历史和裂缝长度历史的渐近表达式，显示初始预应力 tau(0)、摩擦条件（比率 a/b）、水力特性和注入历史如何控制流体诱发的抗震滑动事件的动力学。 (C) 2019 Elsevier Ltd. 保留所有权利。
This study is dedicated to the dynamics of slow slip (or creep) reactivation on faults stimulated by a fluid injection. Fluid driven slow slip events involving slip rates too small to generate detectable elastic waves (typically less than 1 cm.s(-1)) are commonly observed on natural faults either in tectonic active areas or in the framework of deep energy exploitation. We model the fault as a planar 2D velocity strengthening rate-and-state frictional interface embedded in an elastic medium. The fluid is injected at a constant rate and spreads diffusively along the fault reducing the effective normal stress. We show that the fluid injection initiates a shear crack on the fault. In a first phase, the shear crack remains confined to the pressurized zone, and slip-rate increases exponentially with time. A second phase starts at the onset of a rapid crack expansion. The shear crack during phase two expands faster than the pressurized zone. Depending on the prestress conditions, the shear crack evolves towards two different regimes. If the initial shear stress ro is larger than the steady-state residual frictional stress tau(r) within the crack, the slip rate and the crack expansion rate blow up in a finite time. This accelerating crack regime is similar to the nucleation of a dynamic rupture on the fault. On the other hand, if tau(0) < tau(r) the accelerated expansion progressively slows down so that the crack enters a steady regime, characterized by a constant expansion speed and a logarithmic increase of slip-rate. However, a large majority of fault scenarios ultimately lead to this steady expansion regime, which is also the most probable scenario on real tectonic faults. In addition to the numerical results, we develop asymptotic expressions for the maximum slip rate history on the fault and the crack length history, showing how initial prestress tau(0), frictional conditions (ratio a/b), hydraulic properties and injection history control the dynamics of fluid induced aseismic slip events. (C) 2019 Elsevier Ltd. All rights reserved.