Review: Induced Seismicity During Geoenergy Development—A Hydromechanical Perspective.

The basic triggering mechanism underlying induced seismicity traces back to the mid‐1960s that relied on the process of pore‐fluid pressure diffusion. The last decade has experienced a renaissance of induced seismicity research and data proliferation. An unprecedent opportunity is presented to us to synthesize the robust growth in knowledge. The objective of this article is to provide a concise review of the triggering mechanisms of induced earthquakes with a focus on hydro‐mechanical processes. Four mechanisms are reviewed: pore‐fluid pressure diffusion, poroelastic stress, Coulomb static stress transfer, and aseismic slip. For each, an introduction of the concept is presented, followed by case studies. Diving into these mechanisms sheds light on several outstanding questions. For example, why did some earthquakes occur far from fluid injection or after injection stopped? Our review converges on the following conclusions: (a) Pore‐fluid pressure diffusion remains a basic mechanism for initiating inducing seismicity in the near‐field. (b) Poroelastic stresses and aseismic slip play an important role in inducing seismicity in regions beyond the influence of pore‐fluid pressure diffusion. (c) Coulomb static stress transfer from earlier seismicity is shown to be a viable mechanism for increasing stresses on mainshock faults. (d) Multiple mechanisms have operated concurrently or consecutively at most induced seismicity sites. (e) Carbon dioxide injection is succeeding without inducing earthquakes and much can be learned from its success. Future research opportunities exist in deepening the understanding of physical and chemical processes in the nexus of geoenergy development and fluid motion in the Earth's crust. Plain Language Summary: Earthquakes can be triggered by fluids injected into deep underground. Critical knowledge on how they happened has been accumulating since the mid‐1960s after a magnitude 5 earthquake shook Denver, CO, USA. The main culprit is the pore‐fluid pressure in rocks weakening and reactivating existing faults, which leads to earthquakes. The last decade has experienced a renaissance of fluid triggered seismicity research due to the robust development of oil and gas as well as exploration of geothermal energy. This article reviews four processes that contribute to triggering earthquakes: pore‐fluid pressure from injection weakening faults, poroelastic stresses from injection, stresses from earlier earthquakes, and cumulating stresses from aseismic slip. Discussions are presented to address several outstanding questions, for example, why did some earthquakes occur far from fluid injection or after injection? The review leads to following conclusions. (a) Pore‐fluid pressure diffusion remains important for initiating earthquakes near injection. (b) Poroelastic stresses and aseismic slip contribute to inducing seismicity far from injection. (c) Stresses from earlier earthquakes can increase stresses on mainshock faults. (d) Multiple mechanisms often operate to induce earthquakes. (e) CO2 injection is succeeding without inducing earthquakes and lessons can be learned. Future research opportunities exist in understanding induced earthquake hazards. Key Points: Pore‐fluid pressure diffusion remains a basic mechanism for initiating induced seismicity in the vicinity of fluid injectionPoroelastic stress, Coulomb static stress, and aseismic slip also contribute to triggering seismicity beyond the influence of pressure diffusionResearch opportunities exist in developing fully coupled models and integrating process‐oriented models to study induced seismic hazard [ABSTRACT FROM AUTHOR]