A new, robust seismic hazard model and seismic hazard maps for the UK offshore Exclusive Economic Zone using the latest available data and recent advances in seismic hazard methodology and a Monte Carlo-based approach for probabilistic seismic hazard analysis. These are intended to update the current maps for UK waters published in 2002. We developed a comprehensive catalogue of earthquake activity across the region by combining existing earthquake catalogues and data from regional and local monitoring agencies. We modelled earthquake occurrence across the region using a seismic source characterisation (SSC) model that consists of a series of zones, where seismicity is considered to be homogeneous, based on tectonics, geology and seismicity of the study area. We use four different seismic source zone models within the SSC to capture the epistemic uncertainty in different rupture scenarios. A logic tree approach was used to account for the epistemic uncertainty in earthquake activity rates, maximum magnitude, earthquake depth distribution, and faulting style. Ground motions are estimated for different rupture scenarios using a ground motion characterisation (GMC) model that consists of five multiple ground motion prediction equations considered to be applicable to the region. The GMPEs are included in a logic tree where the weights are informed by the fit between observed and modelled ground motions. The GMC model also includes the host-to-target adjustments and a single-station sigma model. Hazard is calculated at 4585 individual points spaced at 0.125° in latitude and 0.25° in longitude for peak ground acceleration (PGA) and spectral acceleration at 0.2 s (SA0.2 s) and 1.0 s (SA1.0 s) for 5% damping and rock conditions and the return periods of 95, 475, 1100, 2475, and 5000 years. This is the first time that maps of the seismic hazard at short (0.2 s) and long periods (1.0 s) have been produced for UK waters. Hazard curves, uniform hazard spectra, and disaggregation analysis have been calculated for three offshore carbon capture and storage sites (Endurance, Acorn, and HyNet North West). New offshore hazard maps for the UK waters will support UK decarbonisation by providing owners and operators of offshore structures with robust estimates of seismic hazard for new and existing sites. The results will also inform regulatory decisions to ensure safe operating practices in the industry and help identify areas of higher hazard where further site-specific studies might be needed. Finally, it will provide a robust baseline for tectonic seismic activity in the North Sea that can be used to help discriminate any seismicity induced by operations, such as CCS, in the event it occurs. The technical report by Mosca et al. (2024), which provides a detailed description of the methods and results, together with the project’s products, can be found in (http://www.earthquakes.bgs.ac.uk/hazard/UKhazard.html).
