The choice of attenuation relationships is one of the most important parts of seismic hazard analysis as using a different attenuation relationship will cause significant differences in the final result, particularly in near distances. This problem is responsible for huge sensibilities of attenuation relationships which are used in seismic hazard analysis. For achieving this goal, attenuation relationships require a good compatibility with the target region. Many researchers have put substantial efforts in their studies of strong ground motion predictions, and each of them had an influence on the progress of attenuation relationships. In this study, two attenuation relationships are presented using seismic data ofMazandaran province in the north of Iran by Genetic Expression Programming (GEP) algorithm. Two site classifications of soil and rock were considered regarding the shear wave velocity of top 30 meters of site. The quantity of primary data was 93 records; 63 of them were recorded on rock and 30 of them recorded on soil. Due to the shortage of records, a regression technique had been used for increasing them. Through using this technique, 693 data had been created; 178 data for soil and 515 data for rock conditions. The Results of this study show the observed PGA values in the region have high correlation coefficients with the predicted values and can be used in seismic hazard analysis studies in the region.
