Incorporating Site Response into Seismic Hazard Assessments for Critical Facilities: A Probabilistic Approach

Abstract

Probabilistic seismic hazard analysis (PSHA) is now the standard approach for developing earthquake ground motions for seismic design because it takes into account the important sources of uncertainty and variability associated with ground motion prediction. PSHA typically does not account for local site response but rather provides a uniform hazard spectrum that is used as the input into site response analyses. This approach does not account rigorously for the uncertainties in the site response analysis, and therefore the resulting surface motion is associated with an unknown hazard level. Seismic hazard assessments for critical facilities, such as nuclear power plants, require that ground motions be defined for specified hazard levels and also include the effects of local site conditions. To achieve this objective, the uncertainty and variability in the site amplification must be quantified and incorporated into the PSHA. This paper describes the convolution approach used to incorporate site response into PSHA. The main components used in the convolution approach are provided, and the required site characterization and site response analyses are discussed. The convolution approach is illustrated through examples from recent projects.