<p>Offshore wind energy is increasingly recognised as a vital source of renewable energy worldwide, with offshore wind farms currently being operated and developed in regions of moderate to high seismic activity. However, there is still limited data on how large-scale offshore wind turbines perform during earthquakes, highlighting the need for further research. This study focuses on the assessment of the seismic performance of large-scale jacket-supported offshore turbines, which have received less attention compared to monopile-supported turbines, and can offer a more attractive solution in seismic regions. Using a risk-based approach, this study investigates the seismic acceleration demands at the rotor-nacelle assembly (RNA) level for a four-legged, X-braced reference steel jacket structure supporting a 10-MW turbine, acting as a representative example of existing and future large-scale jacket-supported offshore wind turbines. The structure is assumed to be located in a reference site in a highly seismically active region, where the hazard is driven by different source types. Particular focus is given to the associated hazard-consistent ground-motion selection methodology considering combined horizontal and vertical ground-motion excitation at different seismic intensity levels that is required for the proper evaluation of the structural system response. 300 nonlinear response history analyses are conducted where the performance is evaluated against a representative range of RNA acceleration limits for which conditional fragility curves are developed. Moreover, to aid in further damage and loss assessments of such structures, a demand curve showing the annual rate of exceeding different demand values is reported. In addition, the contribution of higher-mode response including vertical system excitation is discussed. Finally, in order to relate the acceleration demands to potential structural damage levels, buckling strength evaluations for the support tower are presented and discussed.</p>