Simultaneous separation of source, propagation path, and local site effects from observed strong motion records is carried out by an inversion method in the frequency range from 0.5 to 20 Hz for the purpose of empirical evaluation of the local site effects in different geological conditions. The analyzed data are S-wave portions of 74 accelerograms from 18 events observed at 14 sites in northwestern part of Turkey. These events are shallow earthquakes with magnitude from 3.0 to 5.2 and hypocentral distance from 10 to 90 km. A linear inversion method is applied to the logarithm of the observed spectra, and solutions for source spectra, inelasticity factor of propagation path for S-waves (Qs-value), and factor of site amplification at each site are obtained in least squares sense. In the inversion, we assumed the factor of site amplification at the reference site 1101 is the same as that of theoretical amplification of S-waves to the soil model whose bottom layer has an S-wave velocity (Vs) around 2100 m/s. The factors of site amplification Gj(f) obtained in the present study at each site are verified by comparisons with the theoretical transfer functions. The estimated Qs-value of the propagation path is modeled as Qs(f )=49.28f0.86. Furthermore, we compare the amplifications with average Vs in top 30 meters of the S-wave profiles (Vs30) and proposed linear empirical formula between them at each frequency.