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Abstract

One of the most commonly used parameters to describe seismic attenuation is the high-frequency spectral decay parameter Kappa (κr), yet the physics behind it remain littleunderstood. A better understanding of potential factors that lead to large scatter in esti-mated values ofκrconstitutes a critical need for ground-motion modeling and seismic haz-ard assessment at large. Most research efforts to date have focused on studying the site-to-site and model-to-model variability ofκ, but the uncertainties in individualκrestima-tions associated with different events at a selected site (which we refer to as the within-station variability ofκr) remain uncharacterized. As a direct corollary, obtaining robust esti-mates of the site-specific componentκ0, and their corresponding interpretation become achallenge. To understand the sources of the variability observed inκr(andκ0) at a singlesite, we select 10 Japanese Kiban–Kyoshin network (KiK-net) downhole arrays and inves-tigate the systematic contributions from ground-motion directionality. We observe thatκrestimated from a single horizontal component is orientation dependent. In addition, theinfluence of ground-motion directionality is a function of local site conditions. We proposean orientation-independentκr-value, which is not affected either by ground-motion direc-tionality or by the events’azimuths. In addition, we find that focal depth of events used inκrcalculations affects the estimation of the regional attenuation componentκR, which, inturn, influences the within-station variability in theκ0model.