An Empirical Model for the Interfrequency Correlation of Epsilon for Fourier Amplitude Spectra

An empirical ground-motion model (GMM) is presented for the interfrequency correlation of normalized residuals, epsilon (epsilon), for smoothed Fourier amplitude spectra (FAS). The interfrequency correlation of epsilon (rho(epsilon)) model is developed for the smoothed effective amplitude spectrum (EAS), as defined by Pacific Earthquake Engineering Research Center (PEER; Goulet et al., 2018). The EAS is the orientation-independent horizontal-component FAS of ground acceleration. Ground-motion data are from the PEER Next Generation Attenuation-West2 database (Aneheta et al., 2014), which includes shallow crustal earthquakes in active tectonic regions. The normalized residuals are obtained from the Bayless and Abrahamson (2018b) GMM and are partitioned into between-event, between-site, and within-site components, and a model is developed for the total correlation between frequencies. The total correlation model features a two-term exponential decay with the natural logarithm of frequency. At higher frequencies, the model differs substantially from previously published models, in which the ground-motion smoothing technique used has a large effect on the resulting correlations. The empirical rho(epsilon) is not found to have statistically significant magnitude, distance, site parameter, or regional dependence, although potential regional variations should be studied further. The model is applicable for crustal earthquakes in active tectonic regions worldwide, for rupture distances of 0-300 km, M 3.0-8.0, and over the frequency range 0.1-24 Hz. Tables for the total correlation model coefficients and covariance matrices are provided in the (E) supplemental content to this article.