Offshore wind farms are being planned and constructed in regions throughout the world prone to strong earthquakes which can be a leading design criteria for an offshore wind turbine (OWT). Wind turbines is a highly dynamic structure due to a slender tower which is connected to a heavy mass at the top consisting of nacelle, rotor and rotating blades. Strong earthquakes result in strong ground shaking which will oscillate the OWT and the ground shaking can lead to soil liquefaction. Ground shaking and soil liquefaction can result in unacceptable large deformations of the OWT foundation and is an important design aspect in seismic active regions. The aim of this project is to investigate seismic analysis procedures according to EN 1998-1 and DNV-RP-0585. The first part of the project concerns the seismic analysis procedures in EN 1998-1 where a simple 2D multistory building is exposed to an earthquake and the analysis procedures are compared and discussed. The second part of the project concerns the seismic analysis procedures in DNV-RP-0585 where an OWT foundation located in Japan is exposed to an earthquake. The OWT foundation is modelled as a jacket substructure with embedded piles in three different ways with increasing model complexity and the response in the models are compared. The first model is very simple with rough assumptions about the soil-structure interaction and the last model is more complex and realistic as a soil volume is modelled. The models are made in the software programs SeismoStruct and Plaxis where non-linear dynamic analyses of the OWT foundation are performed. An advanced numerical model of the soil profile are made in the software program DeepSoil to conduct a Site Seismic Response Analysis (SSRA) for assesment of the depth varying ground motions and change in stiffness properties of the soil which are used to asses the response of the OWT foundation. The initiation of soil liquefaction is investigated and compared for a simple approach and an advanced liquefaction model.