On the spatial variation of seismic ground motions and its effects on lifelines

Abstract The effect of the spatial variability-incoherence and apparent propagation of the seismic ground motions on the response of buried and above-ground lifelines is analysed. Simulations based on the most commonly used spatial variability models are generated and the correspondence between the characteristics of the models and those of the space-time simulations is identified. The correlation between the degree of exponential decay in the incoherence of the motions and the response of the structures is determined. It is shown that seismic ground motions that are partially correlated at low frequencies induce the highest quasistatic internal forces in lifelines, whereas motions with slowly decaying incoherence produce the highest contribution to the dynamic response. The significance of the incoherence and the apparent propagation of the motions on the response of the structures is also examined. The apparent propagation of the motions affects the response considerably at low apparent propagation velocities. For higher values of the velocity and for seismic motions that exhibit loss of coherence, the apparent propagation of the motions produces a lower-order effect compared to that of their incoherence for the structures analysed. The most important effect of the spatial incoherence is the introduction of significant quasistatic internal forces in the structures.