Variability in Kappa ($${{\varvec{\kappa}}}_{{\varvec{r}}}$$) Estimated with Coda Waves for California

Abstract

AbstractCharacterizing and quantifying the effects of local soil conditions are essential for site-specific seismic hazard assessment and site response analysis. The high-frequency spectral decay parameter \({\kappa }_{r}\) and its site-specific component, \({\kappa }_{0}\), have gained popularity due to their abilities to characterize near-surface attenuation in situ. Values of \({\kappa }_{0}\) for rock conditions are of particular interest for site-specific seismic hazard analysis for critical facilities. However, ground motions (GM) recorded at sites underlain by stiff soils or rocks are scarce, which limits the computation of \({\kappa }_{0}\) values via the classic acceleration spectrum method. Recent research has found that \(\kappa \) values computed using the coda wave of a GM (i.e., the multiple-scattered wave that is less sensitive to the earthquake source and local site effects) can capture regional variations of the attenuation of hard rock materials regardless of the subsurface conditions near the surface. However, there are still large uncertainties in \(\kappa \) estimates based on the coda wave per GM, \({\kappa }_{r\_coda}\), associated with the absence of consistent guidelines for the computation procedure and a user-orientated GM processing protocol. This work uses California GMs to examine the variability associated with the computation process of \({\kappa }_{r\_coda}\), including the choice of onset of the coda wave and its duration. The objective of this paper is to understand and quantify the variabilities in \(\kappa \) values based on coda waves, which has potentially large implications in its applicability in future ground motion models.KeywordsKappaCoda waveVariabilities and uncertaintiesComputation procedure