The spatiotemporal characteristics of infrequent back-arc rifting events, and their relationships to volcanic unrest and other transient processes within the subduction system are not well known. We report 10 spatio-temporal swarms of earthquakes that occurred along ~300 km of the northern and central Taupō Volcanic Zone (TVZ) between March-September 2019. The swarms lack clear mainshock-aftershock distributions, suggesting involvement of magmatic or pressurized fluids. The most energetic swarms occurred beneath the southwestern flank of Whakaari/White Island volcano (WI) and were accompanied by elevated SO2 emissions and ~8 mm southwest displacement of the edifice. Focal mechanisms of the WI swarms suggest horizontal dilation in the direction of tectonic extension achieved by slip along arrays of closely spaced NE-striking normal faults linked by oblique-slip to strike-slip faults. Given the small GNSS displacements, we favor the interpretation that magmatic volatiles were released by changes in crustal stress. Based on the punctuated, cascading nature of swarms along the northern TVZ, we hypothesize that a rapid reduction in the minimum horizontal stress occurred along the entire northern TVZ over ~5 months, leading to widespread unrest. The probable release of magmatic fluids from shallow magma bodies in the vicinity of WI between May and June argues against a causal relation to the December 9, 2019 WI eruption.

Detecting crustal deformation during transient deformation events at offshore subduction zones remains challenging. The spatiotemporal evolution of slow slip events (SSEs) on the offshore Hikurangi subduction zone, New Zealand, during February–July 2019, is revealed through a time-dependent inversion of onshore and offshore geodetic data that also account for spatially varying elastic crustal properties. Our model is constrained by seafloor pressure time series (as a proxy for vertical seafloor deformation), onshore continuous Global Navigation Satellite System (GNSS) data, and Interferometric Synthetic Aperture Radar (InSAR) displacements. Large GNSS displacements onshore and uplift of the seafloor (10-33 mm) require peak slip during the event of 150 to >200 mm at 6-12 km depth offshore Hawkes Bay and Gisborne, comparable to maximum slip observed during previous seafloor pressure deployments at north Hikurangi. The onshore and offshore data reveal a complex evolution of the SSE, over a period of months. Seafloor pressure data indicates the slow slip may have persisted longer near the trench than suggested by onshore GNSS stations in both the Gisborne and Hawkes Bay regions. Seafloor pressure data also reveal up-dip migration of SSE slip beneath Hawke Bay occurred over a period of a few weeks. The SSE source region appears to coincide with locations of the March 1947 Mw 7.0–7.1 tsunami earthquake offshore Gisborne and estimated Great earthquake rupture sources from paleoseismic investigations offshore Hawkes Bay, suggesting that the shallow megathrust at north and central Hikurangi is capable of both seismic and aseismic rupture.

The coupling at the interface between tectonic plates is a key geophysical parameter to capture the frictional locking across plate boundaries, and provides a means to estimate where tectonic strain is accumulating through time. Here, we use both interferometric radar (InSAR) and GNSS data to investigate the plate coupling of the Hikurangi subduction zone beneath the North Island of New Zealand, where multiple slow slip cycles are superimposed on the long-term loading. We estimate the plate coupling across the subduction zone over different observational periods (2, 4, and 10 years) targeting different stages of the slow slip cycles. Our results highlight the importance of the observational period when interpreting coupling maps, notably highlighting the temporal dependence of plate coupling. Through our analysis of multiple geodetic datasets, we demonstrate how InSAR provides powerful constraints on the spatial resolution of plate coupling, even in a region where a dense GNSS network exists.

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.

Earthquake-triggered slow-moving landslides are not well studied mainly due to lack of high-resolution in-situ geodetic observations both in time and space. Satellite-based interferometric synthetic aperture radar (InSAR) has shown potential in landslides applications, however, it is challenging to detect earthquake-triggered slow-moving landslides over large areas due to the effects of post-seismic tectonic deformations, atmospheric delays, and other spatially propagated errors (e.g., decorrelation noises caused unwrapped errors). Here, we present a novel InSAR phase-gradient-based time-series approach to detect slow-moving landslides that triggered by the 2016 Mw 7.8 Kaikōura earthquake. 21 earthquake-triggered large (> 0.1 km 2) slow-moving landslides are detected and studied. Our results reveal decaying characteristics of the temporal evolutions of these landslides, that averagely after 3.9 years since the earthquake, their postseismic velocity will decay 90% and close to pre-seismic level. Our study opens new perspectives for the research of the mass balance of earthquakes and helps reduce associated hazards.

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.