Interim Results from empirical ground motion model evaluation for the NZ National Seismic Hazard Model Update

Abstract

As a part of the ongoing 2022 NZ National Seismic Hazard Model (NSHM) Update, the predictive capabilities of candidate empirical ground motion models are evaluated to ascertain models which provide good prediction for NZ conditions and adequately capture epistemic uncertainty. This study utilizes a recent ground motion database, also developed as a part of the project. A high-quality subset of the database appropriate for ground motion model validation was adopted comprising over 16000 ground motion records from over 800 earthquakes recorded at 340 strong motion stations. Prediction of ground motions from shallow crustal, subduction interface and subduction slab earthquakes are considered. Numerous candidate models are considered from Next Generation Attenuation studies (e.g., NGA-West2 and NGA-Sub), as well as other recent international and NZ-specific studies. Assessment of model prediction bias and standard deviations are presented to provide a summary of model performance. Analyses of source, path and site parameter dependence and an examination of prediction for scenarios beyond the validation data range (e.g., large Mw subduction interface), including a comparison between models for such scenarios, are also summarised. Results from this study are used to inform ground motion modelling decisions in seismic hazard analyses, such as logic tree weights, metamodel development, and non-ergodic backbone modelling efforts.