Risk-based tolerable magnitudes for induced seismicity at subsurface operations in the Netherlands

Abstract

Induced seismicity is a risk that needs to be managed at any subsurface operation. For- ward-thinking strategies should focus on the tolerable magnitude, MTOL, which defines the level of nuisance, damage, and/or likelihood of fatality at which induced seismic- ity is no longer deemed acceptable. In this study, our objective is to derive risk-based MTOL values for all active subsurface operations in the Netherlands, from producing gas fields to geothermal heat licenses and (CO2) storage operations. In the Netherlands, the acceptability criteria generally adopted are for local risks: 1% probability of DS1 damage, 1% probability of DS2 damage, and a probability of an individual dying due to building collapse (Local Personal Risk) of 10-5/year. We estimate MTOL values based on these risk tolerances and find that MTOL values are field/license specific. We compare our MTOL esti- mates-based individual risk results to equivalent aggregate risks in terms of the number of households affected. This analysis shows that designing thresholds solely on local risk metrics would allow for a significant potential impact, in some cases even larger than the impact of the Huizinge earthquake, which arguably led to the abandonment of the large Groningen gas field. We propose that the combination of individual and aggregate risk acceptance criteria aimed at avoiding unacceptable damage and nuisance provides a socially more defendable approach to inform ‘red light’ thresholds in future traffic light protocols. These considerations will also be informative for guiding monitoring improvements, as they can highlight regions that are currently deficient.