A recent overview and analysis shows that increasing amounts of gas drilling at Groningen, the largest gas field in Europe, led to a dramatic rise in regional earthquakes between 2001 and 2013. After a reduction in extraction was introduced by the Dutch Government, earthquake numbers started to fall. Statistical analysis reveals that if high extraction rates were resumed, about 35 earthquakes, with a magnitude (M) of over 1.5 on the Richter scale, might occur annually from the year 2021 onwards, including four with a damaging magnitude of over 2.5.
“Even if extraction was limited to the 2017 rate set by the government (21.6 billion cubic metres – bcm), the annual number of earthquakes would gradually increase again, with an expected all-time maximum M of 4.5, a serious event capable of shaking walls and chimneys, creating considerable damage and posing safety risks to the public.”
Science for Environment Policy explains, 19 July 2018.
2018 Study Abstract
Recently, growing earthquake activity in the northeastern Netherlands has aroused considerable concern among the 600,000 provincial inhabitants. There, at 3 km deep, the rich Groningen gas field extends over 900 km2 and still contains about 600 of the original 2,800 billion cubic meters (bcm).
Particularly after 2001, earthquakes have increased in number, magnitude (M, on the logarithmic Richter scale), and damage to numerous buildings. The man-made nature of extraction-induced earthquakes challenges static notions of risk, complicates formal risk assessment, and questions familiar conceptions of acceptable risk.
Here, a 26-year set of 294 earthquakes with M ≥ 1.5 is statistically analyzed in relation to increasing cumulative gas extraction since 1963. Extrapolations from a fast-rising trend over 2001-2013 indicate that-under “business as usual”-around 2021 some 35 earthquakes with M ≥ 1.5 might occur annually, including four with M ≥ 2.5 (ten-fold stronger), and one with M ≥ 3.5 every 2.5 years. Given this uneasy prospect, annual gas extraction has been reduced from 54 bcm in 2013 to 24 bcm in 2017. This has significantly reduced earthquake activity, so far.
However, when extraction is stabilized at 24 bcm per year for 2017-2021 (or 21.6 bcm, as judicially established in Nov. 2017), the annual number of earthquakes would gradually increase again, with an expected all-time maximum M ≈ 4.5. Further safety management may best follow distinct stages of seismic risk generation, with moderation of gas extraction and massive (but late and slow) building reinforcement as outstanding strategies.
Officially, “acceptable risk” is mainly approached by quantification of risk (e.g., of fatal building collapse) for testing against national safety standards, but actual (local) risk estimation remains problematic. Additionally important are societal cost-benefit analysis, equity considerations, and precautionary restraint. Socially and psychologically, deliberate attempts are made to improve risk communication, reduce public anxiety, and restore people’s confidence in responsible experts and policymakers.