Input Ground Motion Selection for Site Response Analysis at the Port of Wellington (New Zealand)

Semi-empirical liquefaction evaluation procedures have several limitations and challenges when applied to nonstandard soils such as those found in reclaimed land. Hence, there is a growing need and benefit of additionally performing advanced numerical analyses. Such techniques can provide unique insights on the dynamic response of soils which are beyond the scope of simplified procedures. A key issue in applying dynamic analyses for back-analysis of case history records is the determination of appropriate input earthquake motions. In this study, recorded ground motions of three earthquakes at sites around Wellington city are deconvolved and used to derive input motions for 1D site response analysis of the reclaimed land at the port of Wellington, New Zealand (CentrePort). Three of the deconvolved sites sit on native soil deposits 200–600 m away from the port, and one nominal rock site is approximately 1 km away. The deconvolved motions are then used for forward analysis at neighboring sites and rigorously compared to recorded motions to scrutinize the appropriateness of the input motions. Surface ground motions of the three sites within the basin incorporate the effects of the complex basin geometry (i.e., basin-edge effects) which are not present at the nominal rock site. Since 1D site response analysis does not simulate these features, the study finds that the three basin sites provide reasonable estimates of the recorded surface motions for 1D analysis compared to the nominal rock site. The recommendations in this study will inform the definition of input motions for future analyses of case-history sites in CentrePort.