Site condition investigation using horizontal to vertical spectral ratios of Iran strong motion data

In this study, horizontal to vertical spectral ratios (HVSR) have been calculated for strong ground motion data recorded by the Iran Strong Motion Network (ISMN). Then, a uniform and specific procedure is applied for selecting the peak amplitude (A(peak)) and peak frequency (f(peak)) of the average HVSR for each station in the database. Based on this procedure, A(peak) and f(peak) values were estimated at 502 stations of ISMN. Also, the relationships between HVSR parameters and time-averaged shear wave velocity in the upper 30 m (V-S30) have been investigated and these relationships are presented for Iran. The results and uncertainties of these models are compared with other related studies conducted in Japan, North and Central America, as well as previous studies for Iran. Compared to other datasets, the V-S30 model presented for Iran shows the highest V-S30 values among all models. The equation developed in this study can be used to estimate V-S30 at ISMN stations where there is no other site characteristics available. Therefore, the soil type can be classified according to the Standard No. 2800, which is useful in seismic design codes and other related studies.