Seismic swarms produced by rapid fluid injection into a low permeability laboratory fault
Seismic swarms produced by rapid fluid injection into a low permeability laboratory fault
复制标题
DOI：
10.1016/j.epsl.2020.116726
复制
发表时间：
2021-01-06
影响因子：
5.3
通讯作者：
McLaskey, Gregory C.
中科院分区：
文献类型：
--
作者：
Cebry, Sara Beth L.;McLaskey, Gregory C.
来自废水处理、水力刺激或强化地热系统等活动的流体注入降低了断层上的有效正应力并促进了滑动。地震成核模型表明，在低有效正应力的滑动将是稳定的和抗震相反，在地震活动中观察到的增加，往往归因于流体注入。我们进行了实验室实验，使用双轴加载装置，演示如何增加流体压力可以诱导“粘滑”事件沿着预先存在的锯切故障在聚（甲基丙烯酸甲酯）（PMMA）样品。我们比较了滑动事件所产生的外部挤压的样品（剪切触发），由于直接流体注入（流体触发），并研究了注入速率和应力水平的影响。剪切触发的滑移事件开始于一个局部化的成核补丁和滑动顺利加速从缓慢和asesterian到快速和地震。流体触发的滑动事件开始得更为突然，并与一群微小的前震有关。这些前震能够绕过平滑的成核过程，并启动主震，导致突然启动。对这些前震的分析表明，流体快速注入低渗透性断层，促进了应力和强度的不均匀性，这可能导致许多事件的发生，其中一些事件变得很大。我们的结论是，虽然减少有效的正应力稳定断层滑动，快速注入低渗透性断层流体增加多尺度应力/强度的不均匀性，可以启动小地震事件，有可能迅速增长，甚至进入低应力区。(C)2020爱思唯尔B. V.保留所有权利。
Fluid injection, from activities such wastewater disposal, hydraulic stimulation, or enhanced geothermal systems, decreases effective normal stress on faults and promotes slip. Earthquake nucleation models suggest the slip at low effective normal stress will be stable and aseismic-contrary to observed increases in seismicity that are often attributed to fluid injection. We conducted laboratory experiments using a biaxial loading apparatus that demonstrate how an increase in fluid pressure can induce "stick-slip" events along a preexisting saw-cut fault in a poly(methyl methacrylate) (PMMA) sample. We compared slip events generated by externally squeezing the sample (shear-triggered) to those due to direct fluid injection (fluid-triggered) and studied the effects of injection rate and stress levels. Shear-triggered slip events began on a localized nucleation patch and slip smoothly accelerated from slow and aseismic to fast and seismic. Fluid-triggered slip events initiated far more abruptly and were associated with swarms of tiny foreshocks. These foreshocks were able to bypass the smooth nucleation process and jump-start a mainshock resulting in an abrupt initiation. Analysis of these foreshocks indicates that the rapid injection of fluid into a low permeability fault promotes heterogeneous stress and strength which can cause many events to initiate-some of which grow large. We conclude that while a reduction in effective normal stress stabilizes fault slip, rapid fluid injection into a low permeability fault increases multi-scale stress/strength heterogeneities which can initiate small seismic events that have the potential to grow rapidly, even into low stress regions. (C) 2020 Elsevier B.V. All rights reserved.