The thesis surveys forced vibrations originating from dissimilar excitations important for the calculation of earthquake impact on mechanical structures. The following standard procedures and methods (codes of practices) have been depicted, analysed and commented on: static and quasystatic method according to Uniform Building Code (UBC); earthquake resistance of stresses (EUROCODE 8); "Alstom" procedure for assessment of gas and steam turbines` strengths to earthquakes; ISO3010, dynamic and quasydynamic methods. A new quasydynamic method , applied in ""ALSTOM-Karlovac"" [5] , has been introduced and it has proved to be eligible for the majority of mechanical designers. This method uses the records of structure response to earthquakes and transforms them into equivalent excitations for steady-state response. Regulations and standards in many countries, as well as mentioned international standards (UBC, ISO3010, etc.) were analysed with the aim of suggesting standard magnitude of seismic soil acceleration that will comprise regulations in most countries. Upon conducted strength analyses of various turbine designs, the standard seismic acceleration of horizontally and vertically has been proposed. In most cases both acceleration components act on simultaneously. The new procedure for strength verification of turbine mechanical structure has been proposed. The choice of codes of practices depends not only upon the position of frequencies of structure vibrations` modes as regards the frequency range from 0 to 33 Hz, but also on the skills of the designer. The standard dynamic method is compared with the new quasydynamic method on examples of stress calculation of support and air intake manifold of a gas turbine. It has been concluded that the new quasy-dynamic method can successfully be applied for the assessment of turbine design strength to earthquake impact.