Understanding North Sea (Europe) seismicity for risk mitigation of large-scale CO₂ injections

Carbon capture and storage technologies are an essential part of EU’s decarbonisation efforts. Combined with sustainable energy resources, they are necessary to move Europe towards a net zero carbon emissions economy. Currently, several Mt-scale CO₂ storage projects are being developed in the North Sea. Containment risk evaluation includes analysing tectonic earthquake patterns to potentially map faults, reveal their orientation and failure style, invert for stress directions and at later stages, enable the discrimination of natural and induced seismicity. In addition, seismological information may contribute to the geomechanical understanding of the reservoir and caprock response to large-scale CO₂ injection over time.

A wealth of data exists from various European seismological agencies, but much of it has not been analysed collectively. Within the framework of the ACT project SHARP Storage, an extensive unique earthquake bulletin was compiled using seismicity data from all relevant data centres. Preliminary processing included duplicate removal and explosion identification. In total, 15,230 events were recorded between years 1382 and 2022, of which 3,305 were identified as likely or potential explosions. For the remaining events, waveforms are currently being collected as a basis for further analysis, including event relocation and magnitude homogenisation. Both data sets are planned to being made public after finalising the project.

Relocated events, moment tensor inversion, shear-wave splitting measurements, and stress drop analysis will be compared to and complement a review of borehole stress measurements to better gauge the present-day stress field and enhance seismic hazard assessments.