Earthquakes　occur　frequently　in　China＇s　southeast　coastal　areas.　Therefore,　in　this　region,　offshore　wind　turbine　(OWT)　structures　are　highly　likely　to　be　simultaneously　affected　by　wind,　waves　and　earthquakes.　Firstly,　based　on　the　wave　theory　and　Snell＇s　law,　this　paper　deduces　the　formulas　for　the　equivalent　seismic　nodal　force　of　layered　soils　suitable　for　viscoelastic　artificial　boundaries.　Compared　with　a　method　that　employs　an　average　modulus　to　calculate　the　seismic　motion　input　of　layered　soils,　the　proposed　formulas　enable　more　accurate　simulation　of　seismic　wave　propagation　in　layered　soils.　Based　on　the　formulas,　an　integrated　numerical　model　incorporating　a　nacelle,　tower,　monopile　and　layered　seabed　is　established　to　analyse　the　dynamic　response　of　large-diameter　monopiles　of　OWTs　under　stochastic　wind,　wave　and　seismic　loads.　The　analysis　results　show　that　the　displacement　and　stress　responses　under　combined　wind-wave　loads　are　larger　than　those　under　the　individual　wind/wave　load,　showing　obvious　amplification　effects,　but　the　maximum　acceleration　at　the　mudline　indicates　an　inhibitory　effect,　which　is　not　consistent　with　a　superposition　principle.　Under　the　combined　wind-wave-seismic　loads,　the　monopile　acceleration　is　primarily　attributable　to　the　seismic　load,　with　wind　and　wave　loads　mitigating　the　acceleration　response　caused　by　the　seismic　load.　Moreover,　the　seismic　load　has　little　effect　on　the　monopile＇s　stress　but　increases　its　displacement,　especially　at　the　mudline.　Thus,　additional　treatment　for　foundation　deformation　is　needed　for　the　monopile　design　in　seismic　areas.　©　2025