Taupo Volcano, located in the central part of the TVZ (Taupo volcanic Zone), North Island of New Zealand, is one of the most productive Rhyolitic centres in the world. Although its last eruption occurred about 1800 years ago, 16 periods of unrest have been identified including surface deformation, hydrothermal eruptions, and seismic swarms since 1870. The town of Taupo lies on the north-eastern shore of the lake filling the caldera of the volcano and is located close to recent seismic swarms and local surface deformation episodes highlighted in this report. The aim of this work is to study the different periods of episodic deformation, contrasting with the long-term deformation of the Taupo region, in order to constrain the sources generating local deformation. For this, an analysis of GPS (continuous and campaign stations) and InSAR data (from two satellites, EnviSAT and ALOS) was conducted. After correcting the data for several external factors such as subsidence generated by water pumping in the Wairakei-Tauhara geothermal station and displacements associated with slow slip events along the Hikurangi subduction interface, periods of local deformation have been identified. We highlight two periods of uplift with rates of 10 mm/yr in 2004-2008 and in 2011-2013 accompanied by more or less rapid horizontal deformation punctuated by seismic swarms. The geodetic data were inverted to characterize the deformation sources using the GBIS software, allowing the use of different analytical models. In order to explain the different periods of deformation over time, at least three sources at different locations are needed, revealing the presence of different processes at depths ranging from ∼ 10 km to ∼ 0.5 km and whose causes can vary given the complexity of the tectonic context characterizing the region.

Large-scale ground deformation in Iceland is dominated by extensional plate-boundary deformation, where the Mid-Atlantic Ridge crosses the island, and by uplift due to glacial isostatic adjustment from thinning and retreat of glaciers. While this deformation is mostly steady over multiple years, it is modulated by smaller-scale transient deformation associated with e.g., earthquakes, volcanic unrest, and geothermal exploitation. Here we combine countrywide Sentinel-1 interferometric synthetic aperture radar (InSAR) data (from six tracks) from 2015 to 2021 with continuous GPS observations to produce time-series of displacements across Iceland. The InSAR results were improved in a two-step tropospheric mitigation procedure, using (1) global atmospheric models to reduce long-wavelength and topography-correlated tropospheric signals, and (2) modeling of the stochastic properties of the residual troposphere. Our results significantly improve upon earlier country-wide InSAR results, which were based on InSAR stacking, as we use more data, better data weighting, and advanced InSAR corrections to produce time-series of ground displacements instead of just velocities. We fuse the three ascending and three descending track results to estimate maps of near-East and vertical velocities, which clearly show the large-scale extension and GIA deformation. Using a revised plate-spreading and glacial isostatic adjustment models, based on these new ground velocity maps, we remove the large-scale and steady deformation from the InSAR time-series and analyze the remaining transient deformations. Our results demonstrate the importance of (1) mitigating InSAR tropospheric signals over Iceland and of (2) solving for time-series of deformation, not just velocities, as multiple transient deformation processes are present.

Measuring the deformation at the Earth’s surface over a range of spatial and temporal scales is vital for understanding seismic hazard, detecting volcanic unrest and assessing the effects of vertical land movements on sea level rise. Here, we combine ~10 years of InSAR observations from Envisat with interseismic campaign and continuous GNSS velocities to build a high-resolution velocity field of New Zealand. Exploiting the horizontal GNSS observations, we estimate the vertical component of the deformation to provide the vertical land movement (VLM) for the entire 15,000 km-long coastline. The estimated vertical rates show large variability around the country as a result of volcanic, tectonic and anthropogenic sources. Interseismic subsidence is observed in Kaikoura region supporting models of at least partial locking of the southern Hikurangi subduction interface. Despite data challenges in the mountainous regions from landslides, sediment compaction and glaciers, InSAR data shows localised uplift of the Southern Alps.

Anticipating and managing the impacts of sea-level rise for nations astride active tectonic margins requires rates of sea surface elevation change in relation to coastal land elevation to be understood. Vertical land motion (VLM) can either exacerbate or reduce sea-level changes with impacts varying significantly along a coastline. Determining rate, pattern, and variability of VLM near coasts leads to a direct improvement of location-specific relative sea level (RSL) estimates. Here, we utilise vertical velocity field from interferometric synthetic aperture radar (InSAR) data, calibrated with campaign and continuous Global Navigation Satellite System (GNSS), to determine the VLM for the entire coastline of New Zealand. Guided by existing knowledge of the seismic cycle, the VLM data infer long-term, interseismic rates of land surface deformation. We build probabilistic RSL projections using the Framework for Assessing Changes to Sea-level (FACTS) from IPCC Assessment Report 6 and ingest local VLM data to produce RSL projections at 7435 sites, thereby enhancing spatial coverage that was previously limited to tide gauges. We present ensembles of probability distributions of RSL for medium confidence climatic processes for each scenario to 2150 and low confidence processes to 2300. For regions where land subsidence is occurring at rates >2mm yr-1 VLM makes a significant contribution to RSL projections for all scenarios out 2150. Beyond 2150, for higher emissions scenarios, the land ice contribution to global sea level dominates. We discuss the planning implications of RSL projections, where timing of threshold exceedance for coastal inundation can be brought forward by decades.