Bayesian interfrequency and interintensity empirical correlations of horizontal Fourier amplitude spectra using NGA-West2 data

This article presents Bayesian interfrequency and interintensity empirical correlation coefficients of the horizontal Fourier effective amplitude spectrum (EAS) for frequencies ranging from 0.1 to 20 Hz. Interintensity correlations were calculated between the residuals of the EAS ordinates and the residuals of several peak and cumulative intensity measures, including 5%-damped pseudo-spectral acceleration (PSA), peak ground acceleration (PGA), peak ground velocity (PGV), cumulative absolute velocity (CAV), and Arias intensity (AI). The database used in the study consists of shallow crustal earthquakes in active tectonic regions. The correlation coefficients were calculated using bivariate Bayesian inference of the total residuals of ground-motion models developed by the authors. The component correlations were not found to be dependent on the magnitude of the event. Although the total correlations are magnitude-dependent because of the magnitude-dependent variance components used to calculate them, the differences are so small that the total large-magnitude correlations can be used for all magnitudes. The correlations are dependent on the component residual, the number of frequencies, and the type of ground-motion component. The interfrequency between-event correlations have the largest uncertainty and the weakest decrease with frequency away from the reference frequency than the other component correlations. The interfrequency correlations of EAS were found to be more peaked and to decrease faster away from the reference frequency than those of PSA. Nonetheless, EAS and PSA at the same frequency are strongly correlated with one another over a broad range of frequencies. The interintensity correlations between EAS and the other intensity measures are peaked in the mid-frequency range and do not show the same broadband correlation with EAS that PSA does.