Reflections and some questions about assessing the maximum possible earthquake in the long-exploited Groningen gas field
Reflections and some questions about assessing the maximum possible earthquake in the long-exploited Groningen gas field
Seismological Research Letters (August 2023) 94 (5): 2469-2478
- earthquake prediction
- earthquakes
- Europe
- geophysical methods
- ground motion
- induced earthquakes
- Netherlands
- oil and gas fields
- preventive measures
- probability
- public awareness
- recurrence interval
- risk assessment
- risk management
- rupture
- safety
- sensitivity analysis
- statistical analysis
- Western Europe
- Groningen Field
This article is inspired by an official expert reassessment (September 2022), for the next several decades, of the maximum possible earthquake magnitude, M (sub max) , induced by sixty years of extraction from the rich Groningen gas field in the Netherlands. Basic considerations, advisory inputs, and the assessment of M (sub max) are briefly reviewed. Comments and questions are given on the range and weights of possible M (sub max) values, and on probabilities, "weights", as expert degrees of belief. It is argued that plausible shifts in conditional beliefs (e.g., 100% rather than 90% induced) might have led to a lower future maximum-magnitude range (3.5< or =M (sub max) < or =5.5, with average 4.2) than the reported 4.0< or =M (sub max) < or =6.5 with weighted-average 4.6. As a possible event, M (sub max) should have a nonzero probability that (seismo) logically should go down as M (sub max) goes up. Given that M (sub max) weights assigned are based on expert beliefs, are assessors willing to bet-substantially-on the outcome of an M (sub max) the probability of which is being estimated? For the Groningen field, the assumption of a stationary seismic source and M (sub max) may be disputed. Instead, it is proposed that an eventually observable M (sub max) must be related to total-cumulative extraction since 1963. Hence, after Groningen gas extraction has ended in October 2023, M (sub max) will rapidly decrease. Unfortunately missing is a sensitivity analysis to seize the practical meaning of an (decreasing) M (sub max) distribution, for example, for ground motions, seismic risk (including residents' anxiety), and possible building reinforcement. Such implications bolster the requirement that seismic hazard assessment be thoroughly designed, well understood, and clearly communicated.