National Institute for Earth Physics, 12 Calugareni St., P.O. Box MG-2,
031528 Magurele, Bucharest, Romania
In order to study the effects of the local geological features on the seismic
wave spectra, the Power Spectral Density (PSD) of the P waves generated
by intermediate-depth Vrancea earthquakes was analysed. The PSD was determined
for 19 events with magnitudes
ML > 4, recorded at four stations of the Romanian telemetered
seismic network. The frequencies corresponding to PSD maxima were determined
for all the
earthquakes
at each station and the mean frequencies corresponding to various maxima
in PSD functions, were computed, together with their standard deviations.
Following
the idea of a possible correlation between the PSD and the local geological
conditions, these frequencies were assimilated with the frequencies corresponding
to the
maxima of the transfer function of the structure beneath the station. The
good correlation between the mean PSD and the theoretical transfer function
of the
local geology computed using the Thomson-Haskell method, was pointed out.
Key words: site effects, spectral characteristics, power spectral density.