Improving the accuracy of earthquake magnitudes for North Sea seismicity
Tom Kettlety (University of Oxford)
Peter Voss (Geological Survey of Denmark and Greenland)
Daniela Kühn (GFZ Helmholtz-Zentrum für Geoforschung, Norsar)
Evgeniia Martuganova (TU Delft - Civil Engineering & Geosciences)
Johannes Schweitzer (Norsar, Universitetet i Oslo)
Trine Dahl-Jensen (Geological Survey of Denmark and Greenland)
Annie Jerkins (Norsar)
Elin Skurtveit (Norwegian Geotechnical Institute, Universitetet i Oslo)
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Abstract
To effectively design and operate the many CO2 storage projects that are being developed in the North Sea, seismicity needs to be accurately characterised. Measuring seismicity can provide insights into the stress state in the region, fault density and faulting style, as well as fracturing in the overburden. Understanding background seismicity rates is also key to discriminating, determining the risk of, and mitigation against induced seismicity that could result from injection. Communicating earthquake risk is a key challenge in this field, and central to that is the reporting of earthquake sizes or magnitudes. These magnitudes are reported to the public, and thus their integrity needs to be ensured and their uncertainties thoroughly characterised. Magnitudes also are key input into seismic hazard analysis, a necessary step in the site characterisation of CO2 storage projects and other offshore infrastructure. This study compares and re-evaluates the magnitude estimates from a large database of North Sea seismicity compiled by the ACT3 project SHARP Storage. Magnitudes and their associated uncertainties are computed in a consistent manner and compared to the recordings reported by the regional agencies. Systematic differences are explored, and key sensitives are identified. These results will aid in the monitoring of seismicity in the North Sea, risk assessment for CO2 storage and other infrastructure, and the communication of seismic hazard.