Spectral Attenuation of Strong Motions for Near Source Data in Iran

In this paper the attenuation of Iranian strong motions is studied using Iranian strong motions database. This database comprises more than 6000 well recorded three-components data (analog and digital) for which the teleseismic source parameters were available, or calculated by the records. Here, the one-step regression method is used in order to develop the attenuation model. The spectral values of the recorded strong motions in Iran are used to derive the empirical attenuation laws for different response spectral ordinates at different site conditions. The empirical relationships are established for the spectral acceleration as the function of moment magnitude, hypocentral distances, and constant parameter representing the site conditions. The data set consists of 87 three component accelerograms, all recorded in 1975-2003. In this paper the attenuation coefficients are in general accordance with the previous attenuation coefficients established for Iran. However, the spectral values, obtained here, are greater in comparison with those gained by the previous studies (1999 and 2006). The difference might be due to selecting greater motions, recorded in the distances nearer to the seismic source