Development of seismicity and probabilistic hazard assessment for the Groningen gas field

The increase in number and strength of shallow induced seismicity connected to the Groningen gas field since 2003 and the occurrence of a ML 3.6 event in 2012 started the development of a full probabilistic seismic hazard assessment (PSHA) for Groningen, required by the regulator. Densification of the monitoring network resulted in a decrease of the location threshold and magnitude of completeness down to ∼ ML =0.5. Combined with a detailed local velocity model, epicentre accuracy could be reduced from 0.5–1 km to 0.1–0.3 km and a vertical resolution ∼0.3 km. Time-dependent seismic activity is observed and taken into account into PSHA calculations. Development of the Ground Motion Model for Groningen resulted in a significant reduction of the hazard. Comparison of different implementations of the PSHA, using different source models, based on either a compaction model and production scenarios or on extrapolation of past seismicity, and methods of calculation, shows similar results.