Natural and injection-induced seismicity in stable continental regions: Fingerprinting critically stressed fault systems

在过去十年中，北美一些地区因注入流体而诱发的（人为的）地震活动激增，这主要是对水力压裂和盐水处理等工业活动的反应。地震活动率的增加大部分发生在稳定的大陆地区（scr），这些地区至少有6000万年没有经历过主要的构造活动。与板块边界附近的构造活动区相比，scr内断层的动态行为和位置往往是神秘的。这种知识的缺乏是不确定性的主要来源，也是对诱发地震活动的开发前风险评估的障碍。******地震群是表现出活动逐渐增加和减少的地震活动序列。这些序列缺乏大多数大地震所特有的明确的余震。地震群可以在scr中自然发生，并且被认为与“断层阀”行为有关，在薄弱区域内为地壳内深层流体积聚提供管道。群震活动与热液矿床的形成有关，可能是将大量超压流体注入本质上低渗透岩石的特征响应，例如用于开发非常规碳氢化合物资源的水力压裂。******这个假设驱动的研究项目将探索我们可以从自然地震群中了解到的诱发地震活动的风险，以及反过来，诱发地震如何告知我们对scr自然地震周期的理解。该项目将解决与临界应力断层的“指纹”相关的科学挑战，以及与管理和减轻诱发地震活动危害有关的时间敏感的社会需求。将考虑的基本问题包括：如何识别和描绘地震易感断层？对于自然群震活动和水力压裂引起的地震，流体渗透断层的时间尺度和过程是什么？地震破裂后，断层附近的应力场是如何变化的？长期不活动断层与活动断层系统的性质有何不同？当总溶解气体压力超过冒泡压力时，是否会触发与高压页岩相交的断层——类似于某些火山喷发？******该研究项目将为高素质人才提供最先进的跨学科培训。该课程的毕业生将在未来的行业、政府或学术界提供科学领导。通过提出的系统分析，可以更好地了解scr内的断层系统，从而改进自然和注入引起的群震活动的风险模型。

Induced (human-caused) earthquake activity from fluid injection has surged during the last decade in some parts of North America, largely in response to industrial activities such as hydraulic fracturing and saltwater disposal. Most of this increase in seismicity rate has occurred within stable continental regions (SCRs), areas that have not experienced major tectonic activity for at least 60 million years. In contrast to tectonically active regions near plate boundaries, the dynamic behaviour and location of faults within SCRs are often cryptic. This lack of knowledge constitutes a major source of uncertainty as well as an impediment to pre-development risk assessment for induced seismicity. ******Earthquake swarms are seismicity sequences that exhibit a gradual increase and decrease in activity. These sequences lack well-defined aftershocks that are typical of most large earthquakes. Earthquake swarms can occur naturally in SCRs and are thought to be linked to 'fault-valve' behaviour, within zones of weakness that provide conduits for deep fluids to accumulate within the crust. Swarm seismicity has been linked to the formation of hydrothermal ore deposits and may be a characteristic response to the injection of large volumes of overpressured fluids into intrinsically low-permeability rocks, such as hydraulic fracturing for the development of unconventional hydrocarbon resources.******This hypothesis-driven research program will explore what we can learn about the risks of induced seismicity from natural earthquake swarms and, conversely, how induced earthquakes can inform our understanding of natural earthquake cycles in SCRs. This program will address scientific challenges pertaining to the 'fingerprint' of critically stressed faults, as well as time-sensitive societal needs that pertain to management and mitigation of induced seismicity hazards. Fundamental questions that will be considered include: How can earthquake-susceptible faults be recognized and delineated? What are the timescales and processes of fault infiltration by fluids, for both natural swarm seismicity and hydraulic-fracturing induced earthquakes? How does the stress field near a fault change after earthquake rupture? How do the properties of long-inactive faults differ from active fault systems? Do faults that intersect highly overpressured shales become triggered when total dissolved gas pressure exceeds the bubbling pressure -- similar to some volcanic eruptions? ******This research program will provide state-of-the-art yet interdisciplinary training for highly qualified personnel. Graduates of this program will provide future scientific leadership within industry, government or academia. A better understanding of fault systems within SCRs is likely to arise from the proposed systematic analysis, leading to improved risk models for both natural and injection-induced swarm seismicity.