Random Field Models of Spatially Varying Ground Motions

摘要

The spatial variation of ground motion should be carefully considered in the seismic design of buried lifeline facilities, such as pipeline systems and underground tunnels. It may also have significant influence on the seismic response of long-span bridges and widely spread tanks. Two simple variants of standard spectral models are introduced here to reduce data collection and processing needs. The first model chooses a coherence function that varies with separation length but is independent of frequency. The model can be further simplified by assuming an essentially infinite wave propagation velocity; this leads to a second model with time-space separable correlation function. In the second model, the coherence function can be alternatively viewed and estimated as the spatial correlation between simultaneous ground motions. Good agreement is found with observed relative displacements, both root mean square values and maximum values. Finally, while the predicted relative displacements follow the observed trend with separation distance, the data show somewhat more scatter than the stochastic models imply.