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

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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.