Influence of Bedrock Seismic Action Modelling on Microzonation

Seismic microzonation aims to characterize the Local Seismic Response (LSR) of a territory by accounting for the effects of local geological and geotechnical conditions on filtering the seismic motion at the bedrock. The reliability of the resulting microzonation therefore depends not only on the geotechnical model but also on how the seismic input at the bedrock is defined. Current practice generally relies on selecting natural accelerograms from available databases to match a target response spectrum. Although effective in the spectral domain, this approach may not adequately reproduce the time-dependent characteristics of the seismic motion expected at the site. This study investigates the influence of bedrock input-motion modelling on seismic microzonation results. Fully non-stationary artificial accelerograms are generated from the target response spectrum and from records obtained in the neighborhood of the site. Their effects on the LSR are evaluated through one-dimensional linear-equivalent site response analyses and compared with those obtained using or conventionally selected natural accelerograms, or using accelerograms recorded directly at the site. The study also highlights the extent to which the representation of the bedrock seismic input can affect, after the evaluation of LSR, the estimated nonlinear response of regular and irregular multi-story reinforced concrete frames.