Site‐Effects Model for Central and Eastern North America Based on Peak Frequency

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 σ 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 σ comes from the site‐to‐site component of the variability (reduced by 20% on average), whereas the single‐station variability is unaffected.