One key step in calculation of seismic design parameters, is the use of region-specific attenuation relations (e.g. Campbell, [1] and Green & Hall, [2]). One of the world's largest accelerograph networks exists in Iran, with about 1300 installed instruments. In this paper, making use of 160 records out of the 1200 inspected ones, we present attenuation relations for peak accelerations and, for the first time, 5 percent damped spectral accelerations for the Persian Plateau. Records have been selected having a 50 gal acceleration, with known earthquake parameters, complete time history and response spectra. A fault consistent distance measure and a hybrid Mw consistent magnitude definition was adopted. Also effort has been made to distinguish between rock and soil sites by including a site geology term in the regression model. Analysis was done using a non-linear functional form similar to that of Campbell [3]. Comparison of results with Ambraseys and Bommer [4] and Campbell [5] relations show that, in the distances greater than about 10 km the present study gives significantly higher peak accelerations than other relations. Also the distance saturation of accelerations can not be seen in the resulted relationships and attempt to include this effect in the functional form was fruitless. Even the functional form differs significantly from the above mentioned regional and global studies. A similar difference is observable in the study of Ambraseys and Melville ([6], figure 4-21) about the attenuation of intensities in Iran and in Zare and Bard [7] for attenuation of accelerations. This difference deserves to be further investigated and being clarified.
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