A New Site Classification System Based on Strong Motion Analysis in Iran

The recent five earthquakes in Iran offered many good quality strong motion data at 242 Iranian free-field strong motion stations. These data provide a unique opportunity for site effect analysis and the study of a practical site classification system. The horizontal to vertical spectral ratio (HVSR) of S-wave was used to estimate the soil amplification characteristics at the sites. The strong motion station sites were classified using identified site dominant period and geological data according to Japanese code and 2003 IBC provision. Furthermore, the response spectral shape (RSS) method was also employed in site classification mostly for checking purpose. A choice of site class for each strong motion station was made by comparison among different classifications. The station sites were classified into I, II, III and IV categories (from hard to soft), which are comparable to B, C, D, and E in the 2003 IBC provision. A successful comparison between HVSR and RSS results gives a good support to the classification results. Furthermore, the mean of HVSR for all the records from the earthquakes were calculated according to the site classes, and compared with those of pervious studies in Taiwan and Japan. A good conformity among different outcomes used to validate the classification results. Finally, a new classification system for the site categorization in Iran is introduced, and compared with the one proposed in Iranian building code.