Random-vibration models of free-field seismic ground motion for soil-structure interaction

Various methods are used to estimate seismic ground motion for soil-structure interaction (SSI) analyses at nuclear power plants, depending on the specific application. Where data are abundant, as on the west coast of the US, empirical procedures have been applied to predict various measures of ground shaking. To estimate ground motions for magnitudes and distance ranges that are not well-documented with data even on the west coast, numerical procedures that account for characteristics of the fault rupture and the wave travel path have been developed and used. In regions such as eastern North America (ENA) where recordings of strong seismic shaking are few, other methods have been applied with some success. Both in the regions where data are sparse and where they are abundant, random vibration (RV) representations of ground motion have been developed and applied in recent years with considerable success. This method characterizes seismic shaking as a stochastic process with a defined frequency content and specific assumptions about temporal behavior, from which all interesting measures of ground motion (peak parameter values, response spectra, and instrumental magnitude) can be derived with the application of RV concepts. This paper reviews some of the recent applications of RV methods and indicates some areas in which further work is appropriate. The method is also evaluated as a tool for specifying bedrock input motion for SSI analyses