The physical mechanisms of induced earthquakes

Anthropogenic operations involving underground fluid extraction or injection can cause unexpectedly large and even damaging earthquakes, despite operational and regulatory efforts. In this Review, we explore the physical mechanisms of induced seismicity and their fundamental applications to modelling, forecasting, monitoring and mitigating induced earthquakes. The primary mechanisms of injection-induced earthquakes considered important for creating stress perturbations include pore-pressure diffusion, poroelastic coupling, thermoelastic stresses, earthquake interactions and aseismic slip. Extraction-induced earthquakes are triggered by differential compaction linked with poroelastic effects and reservoir creep. Secondary mechanisms include reducing the rock mass strength subject to stress corrosion, dynamic weakening and cohesion loss. However, constraining the maximum magnitude, Mmax, of a potential earthquake on the basis of physical process understanding is still challenging. Common Mmax theories are based on injection volume as the single source of strain, which might not be efficient in seismically active regions. Alternative time-based Mmax models have the potential to explain why some induced earthquake events tap into tectonic strain and lead to runaway ruptures (in which the rupture front extends beyond the perturbed rock volume). Developments in physics-based forecasting and potential future success in mitigation of induced-seismic risk could help increase the acceptance of emerging energy technologies such as enhanced geothermal systems and underground gas storage during the sustainable transition. Induced earthquakes can occur during several industrial activities, including geothermal developments and underground storage. This Review discusses the current physics-based understanding of induced earthquakes and the implications for forecasting, monitoring, seismic hazard and risk assessments and mitigation strategies.