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This study presents a new model for probabilistic seismic hazard assessment based on fuzzy sets theory. To accomplish seismic hazard analysis in the framework of fuzzy sets theory, all of the variables are first converted into Gaussian fuzzy sets using α-cut method. Then, fuzzified variables are used in seismic hazard analysis. Finally, the outputs are defuzzified using center of area method. The method is applied to Tehran region, Iran, and the fuzzy hazard curve is obtained for the site. The curve displays a fuzzy-probabilistic estimate of peak ground acceleration (PGA) over bedrock for the various return periods. PGA values for the region are estimated to be 0.18-0.20 g and 0.42-0.48 g for 50- and 475-year return periods, respectively. The results are given as fuzzy intervals which accommodate the vagueness inherent in the data. [ABSTRACT FROM AUTHOR]