Simulation of spatially incoherent random ground motions

Two techniques for the artificial generation of spatially incoherent Gaussian seismic ground motions are proposed and validated. The simulated motions are homogeneous and stationary, and may be one-, two-, or three-dimensional in space. They satisfy a prescribed, or target, local power spectrum and a target coherency function. Nonstationarity characteristics are introduced by superimposing a time-dependent envelope function to produce a uniformly modulated non-stationary process. The first technique is asymptotic and approximates the coherency function by a Fourier series: it is general and suits any form of spectrum and coherency. The second technique is approximate in the sense that it satisfies the autospectrum everywhere but satisfies the cross spectrum, or the coherency, between successive stations only. The latter technique is computationally very efficient, and may be accurate enough for discretely supported systems such as single-span structures and multispan, simply supported bridges. The techniques proposed may be useful in response analysis of structures, or structural components, for spatially incoherent random processes in the fields of earthquake, ocean, and wind engineering.