Impact of Ergodic versus Nonergodic Seismic Hazard Estimation on the Risk Assessment of Liquefaction-Induced Ground Damage

ABSTRACT The seismic risk assessment of liquefaction-induced ground damage requires the hazard estimation of ground-motion intensity measures (IMs) through probabilistic seismic hazard analyses (PSHA). Current practice implements PSHA using ground-motion models (GMMs) developed under the ergodic assumption, which considers that the distribution of ground-motion IMs over time at a single site is the same as the distribution of ground-motion IMs over space. With the rapid growth of ground-motion databases, recent efforts have shown that ground-motion recordings are affected by location-specific systematic and repeatable effects favoring the transition to nonergodic approaches. However, the impact of using ergodic versus nonergodic PSHA (accounting for source, path, and site repeatable effects) on the risk assessment of liquefaction-induced damage has not been explored, which is the objective of this study. We consider three sites in California with different availability of ground-motion data to investigate the effects of the amount of available information on constraining repeatable effects and how this affects the final risk estimates within a nonergodic approach. In this context, the nonergodic-based estimates are compared against their ergodic counterparts, and insights are shared. The results from site-specific and regional assessments show important differences between ergodic and nonergodic estimates in terms of the mean risk and its uncertainty; the differences are dependent on the amount of data, and highlight the value of information (i.e., data) in nonergodic approaches.