Tolerable magnitudes for induced seismicity at offshore carbon capture and storage projects

• M TOL is the largest tolerable induced earthquake magnitude for a given operation. • M TOL estimates inform and define induced seismicity risk mitigation strategies. • We use ground motion models and fragility functions to compute M TOL . • We compute M TOL for proposed CCS operations in offshore waters around the UK. A bstract Induced seismicity is a risk that must be managed during the development of Carbon Capture and Storage (CCS) projects. A key step in effective management of induced seismicity is the definition of a tolerable magnitude threshold, M TOL , which defines the level at which the nuisance or damage caused by induced seismicity is likely to no longer be tolerated by affected populations. Having established M TOL , induced seismicity mitigation strategies can be implemented with the objective to avoid induced events that exceed M TOL . In this study our objective is to estimate M TOL for CCS developments in the waters around the UK. Siting CCS operations offshore reduces, but does not eliminate, the risks posed by induced seismicity by increasing the distance from exposed populations. For a given induced earthquake location and magnitude, we use ground motion models, nuisance and fragility functions, and population densities, to estimate the numbers of households that would experience different levels of disturbance and damage. We use past cases of induced seismicity that were, or were not, accepted by the public to define risk tolerances based on the numbers of households that experience different levels of disturbance or damage. We sense-check our results through comparison with observed macroseismic impacts from past, natural earthquakes located in the seas around the UK. As expected, we find that the strongest control on M TOL is the distance to the shore from the proposed project. Our results can be used by CCS operators and regulators in designing induced seismicity mitigation strategies for their sites.