Site Effects Model for Central and Eastern North America Based on Peak Frequency
Abstract We develop a regional site effects model for central and eastern North America based on an analysis of the residuals of observed ground motion parameters relative to two regional ground motion prediction equations: one model has a hard rock (site class A) reference site condition, whereas the other is referenced to a B/C boundary site condition (site classification of National Earthquake Hazard Reduction Program) In both cases, the residuals are well described by a site effects model based on site fundamental frequency f peak in which f peak is as determined from the horizontal to vertical component response spectral ratios. Accordingly, we derive an f peak based site amplification model with respect to B/C and hard rock reference site conditions. Implementing the f peak based model, we reduce random variability in amplitudes s by 10% on average, for a selected database from the Next Generation Attenuation East Project, relative to the value obtained when using a generic site effects model parameterized by near surface shear wave velocity (time averaged shear wave velocity in the upper 30 m, V S 30 The reduction in s comes from the site to site component of the variability (reduced by 20% on average) whereas the single station variability is unaffected.