Estimation of κ0 implied by the high-frequency shape of the NGA-west2 ground-motion prediction equations

Abstract

The spectral-decay parameter κ0 is often used to account for the reduction of the high-frequency amplitude of ground motion caused by attenuation within the site profile. In this study, we used the inverse random vibration theory approach described by Al Atiket al.(2014) to calculate Fourier amplitude spectra from predicted values of response-spectral acceleration for all five Next Generation Attenuation (NGA)-West2 ground-motion prediction equations (GMPEs). We used these spectra to estimate κ0 using the spectral-decay method. Each GMPE was evaluated for a National Earthquake Hazard Reduction Program B/C site condition and for default estimates of depth to the top of rupture, hypocentral depth, and sediment (basin) depth. We derived estimates of κ0 for magnitudes ranging from 3.5 to 8.0 and distances ranging from 5 to 20 km and used a mixed-effects model to derive equations for these estimates as a function of magnitude. We also calculated κ0 from the geometric mean of the response-spectral accelerations of the GMPEs to check the sensitivity of the results to the two approaches and found that the values of κ0 derived in this study using a mixed-effects model are in good agreement with these estimates. The values of κ0 obtained in this study do not necessarily represent the physical high-frequency damping within the site profiles used to develop the NGA-West2 GMPEs. Instead, they are intended to represent the high-frequency shape of the median predicted spectral accelerations from the GMPEs. The κ0 model developed in this study can be used in inversions to develop stochastic models that are intended to mimic the predictions from the NGA-West2 GMPEs.

Publication Title

Bulletin of the Seismological Society of America

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