The paper is devoted to the estimability and recordability of seismic events, namely the research of the noise power spectral density (PSD) and its diurnal variation around “Petrozavodsk” seismic station (PTRZ), located within the Onega structure of the Fennoscandian Shield. The estimation of the noise effect on the seismic record is needed for a reliable determination of strength and distance of different seismic events. The seismic noise spectral features should be taken into account during the primary event record processing for the accurate useful signal extraction.