Characterization of the Kappa (κ0) Spectral Attenuation Parameter in the Glaciated Area of the Northeastern United States

Abstract:

The high frequencies of the Fourier amplitude spectra of ground acceleration records show an observable exponential decay with frequency that is controlled by a parameter called Kappa (κ₀). κ₀ represents the attenuation of seismic waves in the top few hundred meters beneath a site, and κ₀ is a function of the site conditions. For hard-rock sites in eastern North America, past studies with a focus on eastern Canada have determined a regional minimum κ₀ of 0 and a maximum value of 0.01. Probabilistic seismic hazard analysis projects require clearly defined reference rock parameters such as κ₀for hazard computations, and it is also necessary to determine κ₀ values for sites with till and soil cover in the northeastern U.S. In this research, we investigate and update the κ₀ value from accelerometer records for glaciated hard-rock sites as well as for sites with glacial and quaternary sediments throughout the northeastern United States. We determine κ₀ using two methods: 1) by determining a linear least-squares fit to acceleration amplitude spectra at high frequencies in frequency/log-amplitude space, and 2) by modifying the κ₀ scaling term in the ground-motion prediction equation (GMPE) model proposed by Hassani and Atkinson (BSSA, 2018) to estimate best-fit values for the terrain-specific conditions of each instrumented site in the northeastern U.S.