Estimating Systematic Source, Site, and Path Effects in Nonergodic Ground-Motion Models: Insights from the Turkish Ground-Motion Database

The development of ground-motion models (GMMs) is transitioning from ergodic to nonergodic approaches, which account for spatially varying and systematic source, site, and path effects. This study uses a robust ground-motion data set and different strategies for estimating nonergodic terms, assessing their interactions in the context of the formulation of nonergodic GMMs. The study results show that different strategies, specifically the sequence for estimating systematic effects, can significantly impact the trade-off between nonergodic terms, leading to different mean and correlation length estimates, but without significantly impacting the final nonergodic standard deviation after removing systematic effects. In this context, a strategy for treating the interaction and trade-off of systematic nonergodic terms is recommended. Specifically, the proposed approach includes an iterative identification of the distance threshold below which path effects are not expected to contribute significantly to other systematic effects, allowing a more robust estimation of site and source effects. The insights gained in this study highlight that developing GMMs extends beyond a mere exercise of statistical inference or statistical fitting, particularly for nonergodic ground-motion modeling.