  The paper presents results of a comprehensive study of ground motions
recorded during the strong earthquakes (moment magnitude Mw > 6) generated
during last 34 years by the seismic source of Vrancea, Romania. By analyzing
over 300 accelerograms, the capacity of different expressions in the literature
to estimate the predominant period of a ground motion is compared. The
correlation between the values obtained from different evaluations is assessed
as well. The dependence of the predominant period of different factors of
influence is analysed. Comparisons are made between the parameters determined
for the same seismic event at different stations, as well as for ground motions
recorded on the same site at successive earthquakes. The results are
interpreted in correlation with the information provided by frequency bandwidth
parameters. Considerations are made on the measure in which the influence on
the frequency content of the source and of local geological conditions can be
separated, for seismic motions recorded on different locations.
