Displacement Hazard Analysis of Earth Structures Affected by Subduction Zone and Shallow Crustal Earthquakes

Common practice for evaluating the seismic performance of earth dams uses design ground motions selected to be consistent with a target design response spectrum, which are subsequently used in dynamic analyses that estimate seismically induced displacements as an index of performance. This approach involves selecting the probability of exceedance of a ground-motion parameter rather than the probability of exceeding the seismically induced displacements. This implicitly assumes that the different response spectra levels (e.g., different $S_A$ hazard levels or $50\mathrm{t}\mathrm{h}$ percentile versus $84\mathrm{t}\mathrm{h}$ percentile ground motions) is correlated to the different levels of seismically induced displacement. This may not always be the case and can be particularly problematic when evaluating earth structures located in a tectonic setting with multiple source types (e.g., subduction and shallow crustal earthquakes). This can lead to high variability in the estimated displacements, making the selection of a representative overall displacement computed from the different source types not immediately clear. In this study, we propose simplified approaches to select representative displacements for dams affected by earthquakes from multiple source types and we evaluate their performance by constructing displacement hazard curves that rely on the conditional scenario spectra (CSS) framework. We illustrate the application of the proposed procedures for a fictitious dam located in Vancouver, British Columbia, and offer recommendations for using the proposed procedures in practice. Finally, we propose a new procedure for selecting a subset of ground motions for use in complex dynamic analyses [e.g., FEM or finite-difference methods (FDM)] based on the deaggregation from displacement hazard curves rather than the deaggregation from elastic response spectra hazard curves.