Abstract
Over 320 induced earthquakes with magnitude M ≥ 1.5, including 38 with M ≥ 2.5 in the Groningen gas field, the Netherlands, are statistically analysed, and their societal impacts and recent policy changes reviewed. Increased seismicity indicates that the 900 km2 large, 3 km deep and 100 m thick sandstone reservoir has become increasingly vulnerable to further extraction, especially after 2001 and 60% depletion of the total 2800 billion 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 M ≥ 1.5 might occur, including 50 with M ≥ 2.5, 6 with M ≥ 3.5, and 1 with M ≥ 4.5. 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 M ≥ 2.5 to some seven or eight, with one expected Mmax ≈ 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.
Highlights
Only EQs with M ≥ 1.5 are considered because these have been reliably recorded since 1991 (M ≥ 1.5 may be called the ‘magnitude of completeness’), and they are most relevant for the gradual development of building damage
Since 1963, steady depletion of the 900 km2 large, 3 km deep and 100 m thick porous sandstone reservoir originally holding 2800 bcm of natural gas has led to increasing compaction and, as apparent after 1990, an ever greater seismic responsivity to further extraction
Uncertain safety risks and residents’ growing anxiety and stress were politically judged to be no longer acceptable, by April 2018 it became clear that annual gas extraction is likely to be rapidly decreased towards 2023 and more slowly thereafter until the level of practically zero bcm in 2030
Summary
Induced earthquakes up to a Richter magnitude M of 5.0 are a well-known phenomenon around projects of hydrocarbon extraction, wastewater injection, and hydraulic fracturing (Grasso 1992; Nicholson and Wesson 1992; Keranen et al 2014; Walsh and Zoback 2015; Weingarten et al 2015; Atkinson et al 2016; Zhao et al 2018), whereby the causes of seismic hazard and the limitation of seismic risk are outstanding topics of international research attention. Foulger et al (2018) document that for hydrocarbon extraction, induced earthquakes generally stay below M 5.0. Foulger et al (2018) document that for hydrocarbon extraction, induced earthquakes generally stay below M 5.0. A recent, long-emerged but deeply investigated example is the induced earthquake activity from decades of. In the Groningen field, light earthquakes (EQs) of magnitude M < 2.5 (Richter) started to occur in 1991, with around 45% of resource depletion. Since they have increased in number and magnitude, especially after 2001 and so far until 2014; see Fig. 3b below. In the province of Groningen (pop. 600,000), the limited depth (3 km) of the EQs, the relatively soft and wet surface soil (clay, peat, sand), and the long repetitiveness of seismic activity all contribute to considerable damage and
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