2026 seismic hazard maps for the United Kingdom, the Channel Islands, and the UK offshore Exclusive Economic Zone

This report updates the 2020 national hazard maps (Mosca et al., 2022) and the 2024 offshore hazard maps (Mosca et al., 2024) for peak ground acceleration (PGA) and spectral acceleration (SA) at 0.2 s and 1.0 s with 5% damping for the United Kingdom (UK) onshore, including the Channel Islands, using the 2024 offshore seismic hazard model (Mosca et al., 2024) and a Monte Carlo-based approach for probabilistic seismic hazard assessment. It also includes the seismic hazard maps for an additional SA, i.e. SA0.15 s, for the United Kingdom, the Channel Islands, and the UK offshore Exclusive Economic Zone. The maps described in this report are referred to as “2026 seismic hazard maps”.
After a brief description of the 2024 offshore seismic hazard model, I describe the 2026 seismic hazard maps in the UK region for four ground motion parameters, i.e., peak ground acceleration (PGA), spectral acceleration at 0.15 s (SA0.15 s), 0.2 s (SA0.20), and 1.0 s (SA1.00 s), and five return periods (95 years, 475 years, 1100 years, 2475 years, and 5000 years). It is the first time that hazard estimates are provided for a 5000-year return period and the UK onshore. Overall, the 2026 hazard maps confirm that seismic hazard in the UK region is generally low by worldwide hazard standard and increases slightly in regions of higher observed seismic activity, such as North Wales, the Welsh Marches, the northern North Sea, and the southern North Sea around the Dogger Bank area, where the largest (5.9 moment magnitude) instrumentally recorded earthquake occurred. The highest hazard is observed around the region of Snowdonia, in North Wales, and in the northern North Sea. For a 475-year return period, these values are 0.06-0.07 g for PGA, 0.16-0.19 g SA0.15 s, and 0.13-0.16 g for SA0.20 s, and 0.02 g for SA1.00 s; whereas, for 2475 years, they are 0.19-0.21 g for PGA, 0.48-0.52 g SA0.15 s, and 0.39-0.42 g for SA0.20 s and 0.05 g for SA1.00 s.
The report also includes site-specific hazard results (hazard curves, uniform hazard spectra, disaggregation analysis) for selected locations in the UK mainland (i.e. Cardiff, Dover, Edinburgh, and London) and a comparison of these site-specific results with those published in Mosca et al. (2020, 2022) using the 2020 national seismic hazard model. In general, there is an increase in hazard for all ground motion parameters at all sites, except for the PGA, SA0.15 s, SA0.20 s hazard curves at Dover. This is due to the differences between the two hazard models, which are discussed extensively in Mosca (In preparation).
The 2026 seismic hazard map for 475 years, and SA0.15 s is used to calibrate the design seismic requirements of the second-generation Eurocode 8 to the hazard levels of the UK (BS NA EN 1998-1, 2026; PD6698, 2026).