International Institute of Earthquake Engineering and SeismologyJournal of Seismology and Earthquake Engineering1735-166923320210801Investigation of Characteristics of Decay Parameters Kappa Based on Iranian Dataset1970105210.48303/jsee.2023.560541.1021ENAmir HosseinShafieeAssistant Professor, Faculty of Civil Engineering and Architecture, Shahid Chamran University of Ahvaz, Ahvaz, IranHamidZafaraniProfessor, Seismological Research Center, International Institute of Seismology and Earthquake Engineering (IIEES), Tehran, Iran0000-0002-4431-9692MaryamVajdi BilesavarInternational Institute of Seismology and Earthquake Engineering (IIEES), Tehran, IranJournal Article20220820The decay parameter <em>κ</em> (Kappa) which was, first, presented by Anderson and Hough (1984) is commonly used to represent the observed decay of acceleration spectrum at high frequencies. It is considered that <em>κ</em> has a direct linear relationship with distance. The intercept of this line is called <em>κ</em><sub>0</sub>, which is a site-dependent component, and it is supposed to be due to attenuation of seismic waves in near-surface layers. Nowadays, these decay parameters have various applications such as estimation of attenuation function in the square-root-impedance method or implementation of host to target method in ground motion prediction equations. However, the characteristics of both <em>κ </em>and<em> κ</em><sub>0</sub> have not been studied, as it deserves.<br /> In the present paper, the decay parameter <em>κ</em> is obtained by the classical approach using 1157 records from all over Iran. The linearity of <em>κ-</em>distance relationship is questioned and investigated for different distances. It is found that the slope of <em>κ-</em>distance relationship reduces significantly at greater distances, and therefore, a linear correlation equation could not predict well enough specially for great distances. Furthermore, the log-likelihood (LLH) criterion is applied to select the best model that correlates <em>κ</em><sub>0</sub> with <em>V<sub>S</sub></em><sub>30</sub> for different seismotectonic provinces of Iran. This criterion which is based on information theory yields that a linear equation can be a better correlation than a rational one. No asymptote value is observed for <em>κ</em><sub>0</sub> at high values of <em>V<sub>S</sub></em><sub>30</sub>. http://www.jsee.ir/article_701052_7ed66544be84503ffebea9520dbc14a4.pdf