Estimation of Site Effect in Zagros on the Basis of Horizontal-to-Vertical Spectral Ratio

The consequences of recent earthquakes show the importance of site conditions. This means that, as well as source and path effects, the recorded data on the ground surface may be affected by site conditions. In general, the overall site effect is the site and crustal amplification functions combined with the near-surface attenuation. Site amplification is estimated by the H/V ratio. Diminishing of the amplitude in the high frequency band may be modeled in terms of the Kappa factor. In this study, two datasets are considered for determining the H/V ratio and the Kappa factor. Using the best available information, recording sites are classified into two main geologic categories: rock (VS30>500m/s) and soil (VS30<500m/s). Correcting the records is done by using the modified wavelet de-noising method. In the frequency domain, this method can attenuate the noise in the whole frequency range of engineering interest while in the time domain it can detect and remove non- stationary noise. Using the modified wavelet de-noising method, it is possible to retrieve a large number of analog acceleration records which was not possible to correct using conventional methods of correction. A linear regression of the κ0v estimates compiled in this study indicates that κ0v about 0.027, 0.025 for the vertical component, for soil and rock site, respectively. Finally, after determining the Kappa factor and site amplification for the rock and soil sites, total site effect was estimated by multiplying two terms.