Backbone Ground‐Motion Models for Crustal, Interface, and Slab Earthquakes in New Zealand from Equivalent Point‐Source Concepts

A ground‐motion model (GMM) that strikes a balance between empirical and simulation‐based approaches is developed in support of the 2022 update of the New Zealand National Seismic Hazard Model. The development follows the backbone approach, comprising a central model to express the median ground motions for earthquakes in New Zealand (NZ), along with upper and lower alternatives to describe its epistemic uncertainty. Aleatory variability of ground‐motion amplitudes about the median is also characterized. Separate GMMs are developed for crustal, interface, and in‐slab earthquakes. The approach taken is to perform a regression analysis of the NZ response spectra database employing a functional form, concepts, and constraints that are drawn from equivalent point‐source simulations. The model parameters that control the scaling of the GMM with magnitude and distance describe source effects (seismic moment and stress parameter), path effects (geometric and anelastic attenuation), and site effects (site shear‐wave velocity). The NZ database provides constraints on the model for M ∼ 4–7, for frequencies from 0.2 to 100 Hz, at distances to ∼400 km. Extension of the GMM to larger magnitudes (M 7–9) is constrained by the Hassani and Atkinson seismological model, which was developed for application to events of M 3–9 and validated in data‐rich regions (California for crustal earthquakes, Japan for interface and slab earthquakes).