A method for seismic qualification of a component of a piston engine or a component of a genset that comprises a piston engine and a generator coupled to the engine, the method comprising the steps of - determining a Required Response Spectrum, RRS, for the component to be qualified, - running the engine or the genset through a predetermined seismic test cycle in an intended normal configuration of the engine or the genset and determining a Reference Response Spectrum, Ref-RS, for the component by means of at least one acceleration sensor, - forming a seismic test configuration so that during running of the engine or the genset, the engine or the genset is subjected to at least one excitation, which is not encountered when running the engine or the genset in the normal configuration i.e. in the intended use of the genset and producing electricity at the desired frequency, and the forming of the seismic test configuration comprising modification of the resonance frequency of the engine or the genset, - running the engine or the genset through the predetermined seismic test cycle in the seismic test configuration and determining a Test Response Spectrum, TRS, for the component to be qualified by means of the at least one acceleration sensor, - on the basis of the Test Response Spectrum and the Reference Response Spectrum, determining a Modification Response Spectrum, MRS, representing vibrations induced by modification from the normal configuration of the engine or the genset to the seismic test configuration, and - comparing the MRS to the RRS and in case the MRS envelops the RRS, i.e. the MRS is above the RRS in a frequency range that includes the natural frequencies of the component, the component is qualified, - wherein the resonance frequency is modified by changing the properties of support elements that support the engine or the genset against a mounting surface. - determining a Required Response Spectrum, RRS, for the component to be qualified, - running the engine or the genset through a predetermined seismic test cycle in an intended normal configuration of the engine or the genset and determining a Reference Response Spectrum, Ref-RS, for the component by means of at least one acceleration sensor, - forming a seismic test configuration so that during running of the engine or the genset, the engine or the genset is subjected to at least one excitation, which is not encountered when running the engine or the genset in the normal configuration i.e. in the intended use of the genset and producing electricity at the desired frequency, and the forming of the seismic test configuration comprising modification of the resonance frequency of the engine or the genset, - running the engine or the genset through the predetermined seismic test cycle in the seismic test configuration and determining a Test Response Spectrum, TRS, for the component to be qualified by means of the at least one acceleration sensor, - on the basis of the Test Response Spectrum and the Reference Response Spectrum, determining a Modification Response Spectrum, MRS, representing vibrations induced by modification from the normal configuration of the engine or the genset to the seismic test configuration, and - comparing the MRS to the RRS and in case the MRS envelops the RRS, i.e. the MRS is above the RRS in a frequency range that includes the natural frequencies of the component, the component is qualified, - wherein the resonance frequency is modified by changing the properties of support elements that support the engine or the genset against a mounting surface.