Spatial coherency is estimated from seismic data recorded at the unique Parkway array in the Wainuiomata Valley, New Zealand, a small alluvial valley surrounded by greywacke outcrops. This dense array consisted of stations on both the sediment basin and the surrounding rock, with station separation distances pertinent for earthquake engineering applications. It is shown that coherency at the site is generally lower than that at flat alluvial sites, and depends on the type of wave dominating the motions, the component (E-W or N-S) of the motions, and the station pair orientation. These observations can have a significant effect on the seismic response evaluation of lifelines, especially bridges, constructed at sites with irregular subsurface topography.
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