Tafreshi, Mehran DavatgariMehran DavatgariTafreshiBora, Sanjay SinghSanjay SinghBoraGhofrani, HadiHadiGhofraniMirzaei, NoorbakhshNoorbakhshMirzaeiKazemian, JavadJavadKazemian2025-08-312025-08-312022-12-0110.1785/01202103152-s2.0-85142641843https://d8.irins.org/handle/IITG2025/25837Spectral parameter kappa (κ) is widely used to model the decay slope of the Fourier acceleration spectrum at high frequencies. This study presents estimates of κ<inf>0</inf>, often referred to as the site-related contribution in κ, for the Iranian strong-motion dataset. For our analysis, we use 2798 acceleration time histories from 325 earthquakes (between 1976 and 2020, inclusive) in the magnitude range M 3–7.4 and recorded over 285 stations at distances up to 100 km. The main objective of this study is to estimate κ<inf>0</inf> and associated uncertainties at Iranian strong-motion stations. We investigate different sources of uncertainty that contribute to the higher scatter in the station-specific measurements of κ<inf>0</inf>. According to our results, the choice of frequency range used to approximate linear decay of acceleration spectrum contributes significantly to measurement-related uncertainty. Moreover, our measurements exhibit regional variations in (average) κ<inf>0</inf> within Iran; in particular, for Zagros, the average κ<inf>0</inf> 0:036 is found to be lower than that for northern Iran (κ<inf>0</inf> 0:044) and central-eastern Iran (κ<inf>0</inf> 0:04). In terms of between-station variability, there is a weak negative correlation between κ<inf>0</inf> and V<inf>S30</inf>. The within-station uncertainty (i.e., standard deviation of κ<inf>0</inf> values at individual stations) is also found to be decreasing with increasing V<inf>S30</inf>. The fundamental frequency of the site (f<inf>0</inf>) also appears to affect both measurement-related uncertainty and between-station variability at stations that exhibit significant 1D soil response behavior.falseArticle194335733046-3062December 202215arJournal17