Simulation of fully nonstationary spatially variable ground motions on a canyon site

A new method of deriving evolutionary power spectral density (EPSD) function on surface of a canyon site with multiple soil layers was proposed. After the power spectral density on the base rock was determined, the auto/cross power spectral density function on site surface can be obtained by using the frequency response function (FRF), and a series of ground motions can then be generated. However, the spectral nonstationarity was neglected because the parameters in the FRF varied only with frequency. In the present paper, the time-varying frequency and damping ratio in FRF for each soil layer were incorporated for the derivation of the EPSDs on the surface. The influence of local site conditions on the coherency loss was considered. Spatially variable ground motions (SVGMs) possessing full nonstationarity were then simulated. A set of verifications was conducted, and the results showed that the proposed method is reliable.