Abstract Seismicity induced by the injection of fluid into the fractured ground is one of the most challenging issues facing geothermal and deep wastewater disposal industries. This paper introduces an energy-based numerical methodology to study roles of fluid injection in triggering rupture (seismic slip) along preexisting faults. The methodology is developed in the Universal Distinct Element Code (UDEC) using its quasi-static and dynamic schemes and calculates the total seismic energy radiated by a rupture when more energy is made available in the system than can be stored or consumed. As an example of the application of the developed methodology, we study effects of fluid injection on rupture dynamics by pressurizing a single fault surrounded by impermeable rock, representing a simplified analogy for the injection process in deep wastewater disposal and geothermal activities. We discuss effects of raising the fluid pressure on initiating rupture over well-oriented (or critically loaded) and misoriented faults. Results show that fluid injection can trigger a rupture along both well-oriented and misoriented faults although the notion of seismicity may be observed along the well-oriented fault as early as the beginning of the injection process. The well-oriented fault generates higher seismic energy magnitude as more energy is available for rupture due to the higher peak shear stress and stress drop on the fault. Making simplifying assumptions, this study also found that fluid can be injected under a high-pressure increment before and after the fault initial activation while the radiated seismic energy remains relatively insignificant. However, gradually increasing the fluid pressure at the onset of rupture reduces the radiated seismic energy by 30%. Comparing the seismic moment and radiated seismic energy for each event reveals that while radiated seismic energy varies between different values of pressure increment, the calculated seismic moment stays constant, showing the possible ineffectiveness of the seismic moment in representing the intensity of injection-induced ruptures.

中文翻译：

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通过计算辐射地震能量模拟注入诱发的地震活动

摘要 流体注入裂缝地层引起的地震是地热和深层废水处理行业面临的最具挑战性的问题之一。本文介绍了一种基于能量的数值方法，以研究流体注入在沿预先存在的断层触发破裂（地震滑动）中的作用。该方法是在通用独特元素代码 (UDEC) 中开发的，使用其准静态和动态方案，并在系统中提供的能量超过可存储或消耗的能量时计算破裂辐射的总地震能量。作为开发方法应用的一个例子，我们通过对被不渗透岩石包围的单个断层加压来研究流体注入对破裂动力学的影响，代表了深层废水处理和地热活动中注入过程的简化类比。我们讨论了提高流体压力对在定向良好（或临界载荷）和定向错误的断层上引发破裂的影响。结果表明，尽管早在注入过程开始时就可以沿着井向断层观察到地震活动的概念，但流体注入可以触发沿井向断层和错向断层的破裂。由于更高的峰值剪切应力和断层上的应力降，定向良好的断层产生更高的地震能量幅度，因为更多的能量可用于破裂。做出简化假设，该研究还发现，在断层初始激活前后，可以在高压增量下注入流体，而辐射的地震能量仍然相对微不足道。然而，在破裂开始时逐渐增加流体压力会使辐射地震能量降低 30%。比较每个事件的地震矩和辐射地震能量表明，虽然辐射地震能量在不同压力增量值之间变化，但计算出的地震矩保持不变，表明地震矩在表示注入诱发破裂强度方面可能无效。