Spatially-varying non-stationary seismic bedrock motions

Abstract

Seismic bedrock motions required for full soil-structure seismic analysis have not always been available and are simulated in this paper. The stochastic bedrock Fourier spectrum used accounts for source spectrum, attenuation, geometrical spreading and source-to-bedrock amplification effects. Earthquake magnitude, geometrical properties of the source and the bed, and geological profile including the source and path rock are the input. The simulation is further enhanced by authors’ new developments as follows. The frequency-dependent source-to-bedrock amplification factor evaluated by a numerical scheme improves the bedrock Fourier amplitude spectrum. The parametric modulating functions obtained for a specific earthquake magnitude and source properties facilitate the spatiality and non-stationarity. The parametric forms of lagged coherency compatible to specific bedrock sites also ensure the spatiality content. The case study consists of three consecutive examples of the same geometry, where the variation of source-to-bedrock amplification factors at several bedrock depths is investigated. The formulated bedrock Fourier spectrum is then validated. The spatially-varying non-stationary site-compatible bedrock motions are finally simulated where the differences between the averaged Fourier spectra of a realization of 100 simulated accelerograms at two bedrock sites are observed.