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In order to incorporate geodetic measurements of contemporary deformation into the 2022 revision of the New Zealand National Seismic Hazard Model (NSHM), we develop strain rate and fault slip deficit rate models derived from New Zealand’s interseismic Global Navigation Satellite Systems (GNSS)-derived velocity field. Four strain-rate maps, derived from different methodologies, underpin elastic deformation models that are based on inversions of strain rate for slip deficit rates on the suite of faults being used in the New Zealand NSHM 2022 fault model. The methodology adopted for the geodetic-based deformation model here is different from the more commonly adopted methods for estimating long-term fault slip rates using elastic block models or fault-based deep-slipping dislocation models. The need to estimate a geodetic slip rate for the large number of often closely spaced faults in the fault model preclude the use of standard block models, and rapid tectonic rotation of the eastern North Island, observed in the velocity field, makes fault-based models (that do not explicitly include block rotations) difficult to implement. The key advantages of the strain-rate inversion approach adopted here are that it obviates the need to model block rotations and is not hindered by the large number of closely spaced faults. Furthermore, the strain-rate inversion method directly estimates the slip deficit rate, which is the difference between the long-term slip rate on the fault and the present-day creep rate. Slip deficit is assumed to drive the rate of interseismic elastic strain accumulation, much of which we assume will be relieved in future earthquakes. We compute strain-rate maps from the GNSS-derived velocity field using two purely statistical methods and two elasticity-based methods. The statistical methods include VELMAP, which solves for a spatially smooth velocity field by balancing the misfit between fitting observed velocities and minimising the Laplacian of the velocity field. The other uses geostatistical methods of variogram analysis and kriging to build realisations of the velocity and strain-rate fields with covariance structure inherent to the observed velocities. The physics-based methods derive a continuous velocity field using elasticity solutions. These methods solve for a distribution of body forces in an elastic thin plate that explain the observed velocity field and then compute the strain-rate field from the estimated distribution of forces. The Vertical Derivatives of Horizontal Stress (VDoHS) method uses the finite element method to compute elastic responses, while the body-force method adopts analytical expressions for the body-force responses. The principal result from the strain-rate maps is that the mean maximum shear strain rate is similar across all methods, while the spatial distribution of dilatation and strain-rate style differs more significantly. The maximum shear strain rate averaged across the country varies between about 0.1 and 0.12 micro-strain/yr (~20% variation) and the dilatation rate between about 0.015 and 0.023 micro-strain/yr (~40% variation). The dilatation rates appear to show the impact of different types of spatial interpolation methods, with VDoHS and body-force results being relatively smooth, while VELMAP and geostatistics are comparatively rougher but with different characteristics. The uncertainties of the four methods are also quite variable and reflect the assumptions of the method, while differences between methods highlight these assumptions. In particular, there are large differences in the strain rates estimated offshore by the various methods. The uncertainties of the VDoHS, body force and VELMAP methods are small relative to the differences between methods, while the geostatistical method has uncertainty larger than the differences. The inversion of strain-rate maps for slip deficit rate is based on the commonly held assumption in nearly every geodetic-based inversion for slip rates that the majority of present-day strain-rate field is elastic strain due to interseismic coupling across actively slipping faults. Under this assumption, the strain-rate field is linearly related to the slip deficit rates on faults. We discretise the New Zealand NSHM 2022 community fault model into rectangular slip patches in an elastic half space and solve for the spatial distribution of slip deficit rates on faults by inverting the four strain-rate maps. We conduct suites of inversions with and without the geologic slip rate model as a prior on slip deficit rates. The differences in slip deficit rate across all four strain-rate map inversions is typically less than 3–4 mm/yr for the high-rate faults. There are some notable differences between the geologic slip-rate model and the slip deficit inversion results. The geodesy-based inversions infer higher slip rates on belts of faults along the major strike-slip systems, including the Alpine Fault, the Marlborough Fault System and the northern part of the North Island Dextral Fault Belt. The geodesy-based inversions also infer systematically higher slip deficit rates on a complex system of reverse and strike-slip faulting in northern Canterbury and on some faults in the Otago region. The geodetic rates are systematically lower along the near-shore part of the Hikurangi margin. The slip deficit rate models explain 70–80% of the total strain-rate field; the remaining 20–30% of the strain-rate field cannot be mapped to slip deficit rates on faults. Residual strain rates that are not explained by slip deficit rates on faults are relatively low, with maximum shear strain rates typically less than about 0.1 micro-strain/yr. However, the residual strain rates are not randomly distributed; there are systematic spatial patterns to the style of the residual strain-rate field. indicating a potential tectonic origin to the residual strain rates. Finally, the depth distribution of slip deficit rate is not well resolved by the inversions on most of the faults. (The authors)

Launched in 2015, the New Zealand volcano supersite provides regular radar acquisitions covering all the major calderas and cone volcanoes which form the Taupō Volcanic Zone (TVZ). This paper documents new InSAR (Interferometric Synthetic Aperture Radar) observation of deformation over the cone volcanoes within the TVZ including the Tongariro Volcanic complex (TVC) and White Island. Observations over White Island support earlier observations indicating that the stability of the crater wall is controlled, at least in part, by the water level in the crater lake with downslope motion of ∼50 mm/yr observed during the latest period of lake drop in early 2019. Deformation over the TVC is dominated by the continued subsidence above the 2012 Te Maari eruption site at rates of ∼30 mm/yr with no evidence of deformation elsewhere. Synthetic models, used to test the potential detectability of magma movement beneath Ruapehu and White Island, suggest that for small volumes (3), intruded over short periods of time, it would be difficult for InSAR data alone to identify their accumulation. These challenges are not unique to New Zealand's volcanoes and are likely to be faced at other volcanic systems globally.

Auckland, New Zealand, home to a third of New Zealanders, is built on top of the Auckland Volcanic Field (AVF): a mostly monogenetic field of 53 known volcanic vents. The personal, societal, and economic cost of a future AVF eruption are likely substantial, depending on location and crisis response and recovery actions. Estimates of the duration of detectable unrest in the leadup to an AVF eruption range from hours to weeks or longer. Volcano monitoring is globally the proven approach to detecting volcanic unrest, and as such AVF volcano monitoring is critical for detection as early as possible to implement crisis response plans. The Determining Volcanic Risk in Auckland (DEVORA) is a multi-agency, transdisciplinary collaborative research programme led by the University of Auckland and GNS Science and funded by the Earthquake Commission and Auckland Council. DEVORA facilitates and supports research towards a much-improved assessment of volcanic hazard and risk in the Auckland metropolitan area, and supports the strategy and rationale for appropriate risk mitigation. Following a decade of focused research on the AVF, with concurrent development in national and international volcano monitoring capabilities, Auckland Council requested that DEVORA organize a workshop to identify and explore novel monitoring techniques, some of which might, through further research, development, and validation, lead to earlier detection of AVF unrest and decreased uncertainty in confirming unrest and likely future activity. Novel in this context means techniques that are not presently established as operational for AVF monitoring. Auckland Council instructed that cost considerations be disregarded, as the participants were not in a position to undertaker cost-benefit analysis for Auckland. The purpose here was to explore the potential benefit cases for novel techniques. The DEVORA novel monitoring techniques workshop was held on 25 October 2018 as part of the annual DEVORA forum; this report summarises workshop findings. The body of the report is technical, containing specifics relevant to the science community who are encouraged to explore promising techniques. We stress that this is a research opportunities scoping workshop report – suggested network configurations are based on expert judgement during the workshop, and not on detailed network design studies. This report is not an endorsement of any particular approach explored in the workshop, for that further research and testing is required to demonstrate the approach is viable. Additionally, while this report is focused on Auckland, the majority of monitoring approaches summarised here are transferable to other volcanoes. The next steps will be to rate the techniques explored here to guide research priorities for further investigation. (auth)

In December 2018, Ambrym Volcano in Vanuatu entered a period of heightened activity, with a marked change in summit lava lake activity and felt seismicity, a summit rift eruption, the appearance of cracks along the eastern rift zone, and other obvious deformation (e.g. uplifted beaches). This heightened activity continued for several weeks and, at the time, there was considerable uncertainty and concern as to how the situation would unfold. This report compiles documents provided to the Vanuatu Meteorology and Geo-Hazard Department (VMGD) via email by GNS Science staff in support of VMGD’s response to the Ambrym crises of December 2018 and January 2019. The aim is to consolidate information, both as a general reference for what was provided at the time and also to refer to during future volcanic crises in Vanuatu and elsewhere. (auth)

Slow slip events (SSEs) are recognized as an important component of plate boundary fault slip, and there is a need for laboratory friction data on natural samples to guide comparisons with natural SSEs. Here, we compile a comprehensive catalog of SSEs observed geodetically at the Hikurangi subduction zone offshore northern New Zealand, and compare it with results of laboratory friction experiments that produce laboratory SSEs under plate tectonic driving rates (5 cm/yr). We use samples from Ocean Drilling Program Site 1124 seaward of the Hikurangi subduction zone to represent the plate boundary that hosts shallow SSEs at Hikurangi. We find that laboratory SSEs exhibit a similar displacement record and range of stress drops as the natural SSEs. Results of velocity step tests, which can be used to evaluate frictional instability based on the critical stiffness criterion, indicate that the slow slip activity at Hikurangi is a form of stably-accelerating slip. Our laboratory SSEs provide an alternative method of quantifying (in)stability by direct measurement of the unloading stiffness during the stress drop. The observed dependence of laboratory SSE parameters on effective normal stress is consistent with critical stiffness theory; however, depth-increasing projections based on laboratory data do not match observations from natural SSEs. These differences are likely related to changing temperature and fault rock composition downdip but also complications related to scaling and/or limited sampling. Scientific drilling recently undertaken at the Hikurangi subduction zone should serve to improve and guide future studies of the role of frictional properties for the occurrence of SSEs.