Rise and reduction of induced earthquakes in the Groningen gas field, 1991-2018: statistical trends, social impacts, and policy change

Over 320 induced earthquakes with magnitude M1.5, including 38 with M2.5 in the Groningen gas field, the Netherlands, are statistically analysed, and their societal impacts and recent policy changes reviewed. Increased seismicity indicates that the 900km(2) large, 3km deep and 100m thick sandstone reservoir has become increasingly vulnerable to further extraction, especially after 2001 and 60% depletion of the total 2800billion cubic meters (bcm). Regardless of stepwise reductions in annual extraction: from 54 bcm in 2013 to 20 bcm in 2018, well-fitting trends over 1991-2018 reveal a steady growth of seismic activity per unit of gas extraction. This would imply that, before full resource depletion, some 500 more earthquakes with M1.5 might occur, including 50 with M2.5, 6 with M3.5, and 1 with M4.5. Meanwhile, thousands of residents have been suffering from advanced building damage, diminishing property values, disturbing home reinforcement, and various stress-related health complaints. This has spurred a cascade of judgements, decisions and actions by responsible authorities during 2013-2018, topped by the Dutch cabinet's March 2018 decision to reduce Groningen gas extraction to below 12 bcm in 2022 and to end all field operations by 2030. This would reduce the remaining number of risky earthquakes with M2.5 to some seven or eight, with one expected M-max approximate to 4.0. Until 2022, however, seismic hazard and risk would only decrease under average' winter conditions. By December 2018, there has been considerable uncertainty about the actual course of decreasing extraction. Meanwhile, a controversial building-reinforcement programme is being greatly reduced.