Abstract
To reduce the probability of future large earthquakes, traffic light systems (TLSs) define appropriate reactions to observed induced seismicity depending on each event's range of local earthquake magnitude (ML). The impact of velocity uncertainties and station site effects may be greater than a whole magnitude unit of ML, which can make the difference between a decision to continue (“green” TLS zone) and an immediate stop of operations (“red” zone). We show how to include these uncertainties in thresholds such that events only exceed a threshold with a fixed probability. This probability can be set by regulators to reflect their tolerance to risk. We demonstrate that with the new TLS, a red-light threshold would have been encountered earlier in the hydraulic fracturing operation at Preston New Road, UK, halting operations and potentially avoiding the later large magnitude events. It is therefore critical to establish systems which permit regulators to account for uncertainties when managing risk.
Highlights
The increasing number of industrial operations related to hydrocarbon extraction, geothermal power production, hydraulic fracturing for shale gas exploitation, wastewater injection, water impoundment, hydrocarbon storage, and mining operations in recent years, and the potential for large-scale subsurface CO2 storage in future, has increased the importance of understanding and de-risking induced seismicity both to the scientific community and to the public who live near such operations (Grigoli et al, 2017)
The station-averaged ML posterior distribution for one source may have a width that spans more than one zone of the traffic light system which indicates that velocity model uncertainties alone can change the traffic light systems (TLSs) zone to which the earthquake is attributed
We implemented a fully Bayesian approach for analysing uncertainties, such as velocity model and source location uncertainties in local earthquake magnitudes and evaluate their influence on decision-making for induced seismicity. We conclude that these uncertainties are important, as they can make a difference of up to one or two magnitude unit, and directly affect operational decisions by potentially moving an earthquake two zones in a traffic light system (TLS) leading to radically different operational outcomes
Summary
The increasing number of industrial operations related to hydrocarbon extraction, geothermal power production, hydraulic fracturing for shale gas exploitation, wastewater injection, water impoundment, hydrocarbon storage, and mining operations in recent years, and the potential for large-scale subsurface CO2 storage in future, has increased the importance of understanding and de-risking induced seismicity both to the scientific community and to the public who live near such operations (Grigoli et al, 2017). In the UK the “amber” and “red” thresholds for induced seismicity related to unconventional oil and gas operations are set to local earthquake magnitudes ML = 0 and ML = 0.5, respectively, and this has led to multiple halts of hydraulic fracturing operations during the past few years (Clarke et al, 2019) and to an immediate moratorium of operations in November 2019
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