Investigation of Characteristics of Decay Parameters Kappa Based on Iranian Dataset

The decay parameter κ (Kappa) which was, first, presented by Anderson and Hough (۱۹۸۴) is commonly used to represent the observed decay of acceleration spectrum at high frequencies. It is considered that κ has a direct linear relationship with distance. The intercept of this line is called κ۰, 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 κ and κ۰ have not been studied, as it deserves.  In the present paper, the decay parameter κ is obtained by the classical approach using ۱۱۵۷ records from all over Iran. The linearity of κ-distance relationship is questioned and investigated for different distances. It is found that the slope of κ-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 κ۰ with VS۳۰ 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 κ۰ at high values of VS۳۰.

کلیدواژه ها:

Kappa factor ، The log-likelihood criterion ، Acceleration spectrum ، Strong Motion ، Middle-east region