Upper Plate and Subduction Interface Deformation Models in the 2022 Revision of the Aotearoa New Zealand National Seismic Hazard Model

Abstract

ABSTRACT As part of the 2022 revision of the Aotearoa New Zealand National Seismic Hazard Model (NZ NSHM 2022), deformation models were constructed for the upper plate faults and subduction interfaces that impact ground-shaking hazard in New Zealand. These models provide the locations, geometries, and slip rates of the earthquake-producing faults in the NZ NSHM 2022. For upper plate faults, two deformation models were developed: a geologic model derived directly from the fault geometries and geologic slip rates in the NZ Community Fault Model version 1.0 (NZ CFM v.1.0); and a geodetic model that uses the same faults and fault geometries and derives fault slip-deficit rates by inverting geodetic strain rates for back slip on those specified faults. The two upper plate deformation models have similar total moment rates, but the geodetic model has higher slip rates on low-slip-rate faults, and the geologic model has higher slip rates on higher-slip-rate faults. Two deformation models are developed for the Hikurangi–Kermadec subduction interface. The Hikurangi–Kermadec geometry is a linear blend of the previously published interface models. Slip-deficit rates on the Hikurangi portion of the deformation model are updated from the previously published block models, and two end member models are developed to represent the alternate hypotheses that the interface is either frictionally locked or creeping at the trench. The locking state in the Kermadec portion is less well constrained, and a single slip-deficit rate model is developed based on plate convergence rate and coupling considerations. This single Kermadec realization is blended with each of the two Hikurangi slip-deficit rate models to yield two overall Hikurangi–Kermadec deformation models. The Puysegur subduction interface deformation model is based on geometry taken directly from the NZ CFM v.1.0, and a slip-deficit rate derived from published geodetic plate convergence rate and interface coupling estimates.