Transient evolution of the relative size distribution of earthquakes as a risk indicator for induced seismicity

Induced earthquakes pose a substantial challenge to many geo-energy applications, and in particular to Enhanced Geothermal Systems. We demonstrate that the key factor controlling the seismic hazard is the relative size distribution of earthquakes, the b-value, because it is closely coupled to the stress conditions in the underground. By comparing high resolution observations from an Enhanced Geothermal System project in Basel with a loosely coupled hydro-mechanical-stochastic model, we establish a highly systematic behaviour of the b-value and resulting hazard through the injection cycle. This time evolution is controlled not only by the specific site conditions and the proximity of nearby faults but also by the injection strategy followed. Our results open up new approaches to assess and mitigate seismic hazard and risk through careful site selection and adequate injection strategy, coupled to real-time monitoring and modelling during reservoir stimulation.

Automated summary

This article investigates the hazards caused by induced earthquakes in enhanced geothermal systems and reveals the importance of the relative size distribution of earthquakes, or the b-value, in controlling seismic risks. By comparing field observations and model results, the study demonstrates the systematic evolution of the b-value and resulting hazard during the injection cycle, which is influenced by site conditions, proximity to faults, and injection strategy. The findings provide new insights for assessing and mitigating seismic hazards and risks in geothermal projects.