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Abstract We investigate the occurrence patterns of SSEs along the shallow (15 km) portion of the Hikurangi subduction zone. First, we build a manual catalog constraining timing and length of 92 SSEs between 2006 and 2024. Then, we investigate SSE occurrence patterns by fitting a renewal process, using Bayesian inference to obtain the posterior distribution of model parameters. Our results show that SSE recurrence intervals vary along the Hikurangi margin; less frequent SSEs occur in the southern part of the margin. The periodicity of SSEs also changes along strike. SSEs in the northern part of the margin occur more regularly than those at the central part. Finally, we do not find conclusive evidence that 2016 7.8 Kaikōura earthquake had a lasting effect on SSE occurrence patterns. 

The Hikurangi margin has been an important global focus for subduction zone research for the last decade. International Ocean Discovery Program drilling and geophysical investigations have advanced our understanding of megathrust slip behavior. Along and across the margin, detailed imaging reveals that the megathrust structure varies spatially and evolves over time. Heterogeneous properties of the plate boundary zone and overriding plate are impacted by the evolving nature of regional tectonics and inherited overriding plate structure. Along-strike variability in thickness of subducting sediment and northward increasing influence of seamount subduction strongly influence mega-thrust lithologies, fluid pressure, and permeability structure. Together, these exert strong control on spatial variations in coupling, slow slip, and seismicity distribution. Thicker incoming sediment, combined with a compressional upper plate, influences deeper coupling at southern Hikurangi, where paleoseismic investigations reveal recurring great (M_w> 8.0) earthquakes.▪The Hikurangi Subduction Zone is marked by large-scale changes in the subducting Pacific Plate and the overlying plate, with varied tectonic stress, crustal thickness, and sediment cover.▪The roughness of the lower plate influences the variability in megathrust slip behavior, particularly where seamounts enhance subduction of fluid-rich sediments.▪Variations in sediment composition impact the strength of the subduction interface, with the southern Hikurangi Subduction Zone exhibiting a more uniform megathrust fault.▪Properties of the upper plate influence fluid pressures and contribute to the observed along-strike variations in Hikurangi plate coupling and slip behavior. 

Abstract The potential for future earthquakes on faults is often inferred from inversions of geodetically derived surface velocities for locking on faults using kinematic models such as block models. This can be challenging in complex deforming zones with many closely spaced faults or where deformation is not readily described with block motions. Furthermore, surface strain rates are more directly related to coupling on faults than surface velocities. We present a methodology for estimating slip deficit rate directly from strain rate and apply it to New Zealand for the purpose of incorporating geodetic data in the 2022 revision of the New Zealand National Seismic Hazard Model. The strain rate inversions imply slightly higher slip deficit rates than the preferred geologic slip rates on sections of the major strike‐slip systems including the Alpine Fault, the Marlborough Fault System and the northern part of the North Island Fault System. Slip deficit rates are significantly lower than even the lowest geologic estimates on some strike‐slip faults in the southern North Island Fault System near Wellington. Over the entire plate boundary, geodetic slip deficit rates are systematically higher than geologic slip rates for faults slipping less than one mm/yr but lower on average for faults with slip rates between about 5 and 25 mm/yr. We show that 70%–80% of the total strain rate field can be attributed to elastic strain due to fault coupling. The remaining 20%–30% shows systematic spatial patterns of strain rate style that is often consistent with local geologic style of faulting. 

ABSTRACT Geodetic data in plate boundary zones reflect the accrual of tectonic strain and stress, which will ultimately be released in earthquakes, and so they can provide valuable insights into future seismic hazards. To incorporate geodetic measurements of contemporary deformation into the 2022 revision of the New Zealand National Seismic Hazard Model 2022 (NZ NSHM 2022), we derive a range of strain-rate models from published interseismic Global Navigation Satellite Systems velocities for New Zealand. We calculate the uncertainty in strain rate excluding strain from the Taupō rift–Havre trough and Hikurangi subduction zone, which are handled separately, and the corresponding moment rates. A high shear strain rate occurs along the Alpine fault and the North Island dextral fault belt, as well as the eastern coast of the North Island. Dilatation rates are primarily contractional in the South Island and less well constrained in the North Island. Total moment accumulation derived using Kostrov-type summation varies from 0.64 to 2.93×1019  N·m/yr depending on method and parameter choices. To account for both aleatory and epistemic uncertainty in the strain-rate results, we use four different methods for estimating strain rate and calculate various average models and uncertainty metrics. The maximum shear strain rate is similar across all methods, whereas the dilatation rate and overall strain rate style differ more significantly. Each method provides an estimate of its own uncertainty propagated from the data uncertainties, and variability between methods provides an additional estimate of epistemic uncertainty. Epistemic uncertainty in New Zealand tends to be higher than the aleatory uncertainty estimates provided by any single method, and epistemic uncertainty on dilatation rate exceeds the aleatory uncertainty nearly everywhere. These strain-rate models were provided to the NZ NSHM 2022 team and used to develop fault-slip deficit rate models and scaled seismicity rate models. 

Key Points Periodic pore fluid pressure perturbations on a rate‐strengthening fault induce slow slip events (SSEs) Source properties of induced SSEs vary with perturbation characteristics (length scale, amplitude, period) Model reproduces source properties of shallow Hikurangi SSEs, and duration and magnitude of SSEs in different subduction zones 

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.