Comment on “Estimating the Maximum Magnitude of Induced Earthquakes in the Groningen Gas Field, the Netherlands” by Julian Bommer, Jan van Elk, and Mark Zoback

In their “Estimating the maximum magnitude of induced earthquakes in the Groningen gas field, the Netherlands,” Bommer, van Elk, and Zoback (BvEZ) present good reasons to revise the 2022 expert-panel assessment of the maximum possible earthquake magnitude (Mmax) in the Groningen gas field, but their timing (August 2024) and authorship are remarkable. Here, it is argued that: (1) induced Mmax arises from a changing seismic source, (2) effective safety communication requires clarification of the practical meaning of “logic tree,” “expert weight,” and “possible” versus “expected,” (3) multivariate sensitivity analysis is needed to appreciate the implications of Mmax, for example, surface (vibratory) ground movements, (4) independent peer review may be useful but too much asked, and that (5) possible conservatism in Mmax assessment may be due to (costly) precautionary reasoning under uncertainty. The importance of balanced multiparty risk communication is emphasized. Concluding remarks are about institutional responsibilities for (apparently) insufficient Mmax assessment in 2022, the implications of BvEZ’s current re-evaluation for further building reinforcement and restoration policies for Groningen, and the desirability of reviving the expert assessment process on Mmax, to validate BvEZ’s main proposal that, for Groningen, 3.6≤Mmax≤4.1. After the field’s recent closure, ever observable Mmax will probably never exceed the historical earthquake magnitude of 3.6 near Huizinge in 2012.