scholarly journals Intermediate-depth earthquakes and the connection of the seismicity with metamorphism and deep fluid regime in subduction zone for the North Island of New Zealand

2020 ◽  
Vol 4 (1) ◽  
pp. 103-115
Author(s):  
M.A. Nikitina ◽  
◽  
M.V. Rodkin ◽  
◽  
◽  
...  
Keyword(s):  
New Zealand ◽  
Subduction Zone ◽  
Fluid Regime ◽  
Intermediate Depth ◽  
The North ◽  
Deep Fluid

Geodetic strain and the deformational history of the North Island of New Zealand during the late Cainozoic

1987 ◽  
Vol 321 (1557) ◽  
pp. 163-181 ◽  
Keyword(s):  
New Zealand ◽  
Subduction Zone ◽  
East Coast ◽  
Late Quaternary ◽  
Plate Boundary ◽  
Boundary Zone ◽  
Metamorphic Belt ◽  
Volcanic Region ◽  
The North ◽  
Plate Boundary Zone

The subduction zone under the east coast of the North Island of New Zealand comprises, from east to west, a frontal wedge, a fore-arc basin, uplifted basement forming the arc and the Central Volcanic Region. Reconstructions of the plate boundary zone for the Cainozoic from seafloor spreading data require the fore-arc basin to have rotated through 60° in the last 20 Ma which is confirmed by palaeomagnetic declination studies. Estimates of shear strain from geodetic data show that the fore-arc basin is rotating today and that it is under extension in the direction normal to the trend of the plate boundary zone. The extension is apparently achieved by normal faulting. Estimates of the amount of sediments accreted to the subduction zone exceed the volume of the frontal wedge: underplating by the excess sediments is suggested to be the cause of late Quaternary uplift of the fore-arc basin. Low-temperature—high-pressure metamorphism may therefore be occurring at depth on the east coast and high-temperature—low-pressure metamorphism is probable in the Central Volcanic Region. The North Island of New Zealand is therefore a likely setting for a paired metamorphic belt in the making.

Relationships of the Seismicity at the Alaska Subduction Zone to Metamorphism and the Deep Fluid Regime

2020 ◽  
Vol 56 (6) ◽  
pp. 892-899
Author(s):  
Margarita A. Nikitina ◽  
Mikhail V. Rodkin ◽  
Ivan G. Shmakov
Keyword(s):  
Subduction Zone ◽  
Fluid Regime ◽  
Deep Fluid

scholarly journals Adjoint tomography of the Hikurangi subduction zone and the North Island of New Zealand

2021 ◽  
Author(s):  
Bryant Chow
Keyword(s):  
New Zealand ◽  
Subduction Zone ◽  
East Coast ◽  
Plate Boundary ◽  
Velocity Model ◽  
Seismic Velocities ◽  
Low Velocity ◽  
Velocity Models ◽  
The North ◽  
Adjoint Tomography

<p><b>Seismic tomography is a powerful tool for understanding Earth structure. In New Zealand, velocity models derived using ray-based tomography have been used extensively to characterize the complex plate boundary between the Australian and Pacific plates. Advances in computational capabilities now allow us to improve these velocity models using adjoint tomography, an imaging method which minimizes differences between observed and simulated seismic waveforms. We undertake the first application of adjoint tomography in New Zealand to improve a ray-based New Zealand velocity model containing the Hikurangi subduction zone and the North Island of New Zealand.</b></p> <p>In support of this work we deployed the Broadband East Coast Network (BEACON), a temporary seismic network aimed at improving coverage of the New Zealand permanent network, along the east coast of the North Island. We concurrently develop an automated, open-source workflow for full-waveform inversion using spectral element and adjoint methods. We employ this tool to assess a candidate velocity model’s suitability for adjoint tomography. Using a 3D ray-based traveltime tomography model of New Zealand, we generate synthetic seismic waveforms for more than 10 000 source–receiver pairs and evaluate waveform misfits. We subsequently perform synthetic checkerboard inversions with a realistic New Zealand source–receiver distribution. Reasonable systematic time shifts and satisfactory checkerboard resolution in synthetic inversions indicate that the candidate model is appropriate as an initial model for adjoint tomography. This assessment also demonstrates the relative ease of use and reliability of the automated tools.</p> <p>We then undertake a large-scale adjoint tomography inversion for the North Island of New Zealand using up to 1 800 unique source–receiver pairs to fit waveforms with periods 4–30 s, relating to minimum waveform sensitivities on the order of 5 km. Overall, 60 geographically well-distributed earthquakes and as many as 88 broadband station locations are included. Using a nonlinear optimization algorithm, we undertake 28 model updates of Vp and Vs over six distinct inversion legs which progressively increase resolution. The total inversion incurred a computational cost of approximately 500 000 CPU-hours. The overall time shift between observed and synthetic seismograms is reduced, and updated velocities show as much as ±30% change with respect to initial values. A formal resolution analysis using point spread tests highlights that velocity changes are strongly resolved onland and directly offshore, at depths above 30 km, with low-amplitude changes (> 1%) observed down to 100 km depth. The most striking velocity changes coincide with areas related to the active Hikurangi subduction zone.</p> <p>We interpret the updated velocity model in terms of New Zealand tectonics and geology, and observe good agreement with known basement terranes, and major structural elements such as faults, sedimentary basins, broad-scale subduction related features. We recover increased spatial heterogeneity in seismic velocities along the strike of the Hikurangi subduction zone with respect to the initial model. Below the East Coast, we interpret two localized high-velocity anomalies as previously unidentified subducted seamounts. We corroborate this interpretation with other work, and discuss the implications of deeply subducted seamounts on slip behavior along the Hikurangi margin. In the Cook Strait we observe a low-velocity zone that we interpret as a deep sedimentary basin. Strong velocity gradients bounding this low-velocity zone support hypotheses of a structural boundary here separating the North and South Islands of New Zealand. In the central North Island, low-velocity anomalies are linked to surface geology, and we relate seismic velocities at depth to crustal magmatic activity below the Taupo Volcanic Zone.</p> <p>This new velocity model provides more accurate synthetic seismograms and additional constraints on enigmatic tectonic processes related to the North Island of New Zealand. Both the velocity model itself, and the underpinning methodological contributions, improve our ever-expanding understanding of the North Island of New Zealand, the Hikurangi subduction zone, and the broader Australian-Pacific plate boundary.</p>

Slow Slip Events in New Zealand

2020 ◽  
Vol 48 (1) ◽  
pp. 175-203 ◽  
Author(s):  
Laura M. Wallace
Keyword(s):  
New Zealand ◽  
Subduction Zone ◽  
Slow Motion ◽  
Plate Motion ◽  
Slow Slip ◽  
Slow Slip Events ◽  
Diverse Range ◽  
The North ◽  
Interseismic Coupling ◽  
Natural Laboratory

Continuously operating global positioning system sites in the North Island of New Zealand have revealed a diverse range of slow motion earthquakes on the Hikurangi subduction zone. These slow slip events (SSEs) exhibit diverse characteristics, from shallow (<15 km), short (<1 month), frequent (every 1–2 years) events in the northern part of the subduction zone to deep (>30 km), long (>1 year), less frequent (approximately every 5 years) SSEs in the southern part of the subduction zone. Hikurangi SSEs show intriguing relationships to interseismic coupling, seismicity, and tectonic tremor, and they exhibit a diversity of interactions with large, regional earthquakes. Due to the marked along-strike variations in Hikurangi SSE characteristics, which coincide with changes in physical characteristics of the subduction margin, the Hikurangi subduction zone presents a globally unique natural laboratory to resolve outstanding questions regarding the origin of episodic, slow fault slip behavior. ▪  New Zealand's Hikurangi subduction zone hosts slow slip events with a diverse range of depth, size, duration, and recurrence characteristics. ▪  Hikurangi slow slip events show intriguing relationships with seismicity ranging from small earthquakes and tremor to larger earthquakes. ▪  Slow slip events play a major role in the accommodation of plate motion at the Hikurangi subduction zone. ▪  Many aspects of the Hikurangi subduction zone make it an ideal natural laboratory to resolve the physical processes controlling slow slip.

scholarly journals Strike-Slip Enables Subduction Initiation Beneath a Failed Rift: New Seismic Constraints from Puysegur Margin, New Zealand

2020 ◽  
Author(s):  
Brandon Shuck ◽  
Harm Van Avendonk ◽  
Sean Gulick ◽  
Michael Gurnis ◽  
Rupert Sutherland ◽  
...  
Keyword(s):  
New Zealand ◽  
Subduction Zone ◽  
Plate Boundary ◽  
Strike Slip ◽  
Rift Basin ◽  
The South ◽  
Subduction Initiation ◽  
The North ◽  
Collision Zone ◽  
Seismic Images

&lt;p&gt;Critical ingredients and conditions necessary to initiate a new subduction zone are debated. General agreement is that subduction initiation likely takes advantage of previously weakened lithosphere and may prefer to nucleate along pre-existing plate boundaries. To evaluate how past tectonic regimes and lithospheric structures might facilitate underthrusting and lead to self-sustaining subduction, we present an analysis of the Puysegur Margin, a young subduction zone with a rapidly evolving tectonic history.&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;&lt;p&gt;The Puysegur Margin, south of New Zealand, currently accommodates convergence between the Australian and Pacific plates, exhibits an active seismic Benioff zone, a deep ocean trench, and young adakitic volcanism on the overriding plate. Tectonic plate reconstructions show that the margin experienced a complicated transformation from rifting to seafloor spreading, to strike-slip motion, and most recently to incipient subduction, all in the last ~45 million years. Details of this tectonic record remained incomplete due to the lack of high-quality seismic data throughout much of the margin.&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;&lt;p&gt;Here we present seismic images from the South Island Subduction Initiation Experiment (SISIE) which surveyed the Puysegur region February-March, 2018. SISIE acquired 1252 km of deep-penetrating multichannel seismic (MCS) data on 7 transects, including 2 regional dip lines coincident with Ocean Bottom Seismometers (OBS) deployments which extend (west to east) from the incoming Australian plate, across the Puysegur Trench and Puysegur Ridge, over the Solander Basin and onto the continental Campbell Plateau margin.&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;&lt;p&gt;We integrate pre-stack depth migrated MCS profiles with OBS tomography models to constrain the tectonic development of the Puysegur Margin. Based on our results we propose the following Cenozoic evolution: (1) The entire Solander Basin contains thinned continental crust which formed from orthogonal stretching between the Campbell and Challenger plateaus during the Eocene-Oligocene. This phase of rifting was more pronounced to the south, producing thinner crust with abundant syn-rift volcanism across a wider rift-basin, in contrast to the relatively thicker crust, moderate syn-rift volcanism and narrower rift basin in the north. (2) Strike-slip deformation subsequently developed along Puysegur Ridge, west of the locus of rifting and within relatively unstretched continental lithosphere. This young strike-slip plate boundary translated unstretched crust northward causing an oblique continent-collision zone, which led to a transpressional pattern of distributed left-stepping, right-lateral faults. (3) Subduction initiation was aided by large density contrasts as oceanic lithosphere translated from the south was forcibly underthrust beneath the continent-collision zone. Early development of oblique subduction generated modest and widespread reactivation of faults in the upper plate. (4) Present-day, the Puysegur Trench shows a spatiotemporal transition from nearly mature subduction in the north to a recently initiated stage along the southernmost margin, requiring a southward propagation of subduction through time.&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;&lt;p&gt;Our new seismic images suggest subduction initiation at the Puysegur Margin was assisted by inherited buoyancy contrasts and structural weaknesses that were imprinted into the lithosphere during earlier phases of continental rifting and strike-slip along the developing plate boundary. The Puysegur Margin demonstrates that forced nucleation along a strike-slip boundary is a viable subduction initiation model and should be considered throughout Earth&amp;#8217;s history.&lt;/p&gt;

scholarly journals Geophysical Constraints on the Relationship Between Seamount Subduction, Slow Slip, and Tremor at the North Hikurangi Subduction Zone, New Zealand

2018 ◽  
Vol 45 (23) ◽  
Author(s):  
Daniel H. N. Barker ◽  
Stuart Henrys ◽  
Fabio Caratori Tontini ◽  
Philip M. Barnes ◽  
Dan Bassett ◽  
...  
Keyword(s):  
New Zealand ◽  
Subduction Zone ◽  
Slow Slip ◽  
The North ◽  
Seamount Subduction ◽  
The Relationship

scholarly journals Seismic Constraint on Heterogeneous Deformation and Stress State in the Forearc of the Hikurangi Subduction Zone, New Zealand

2021 ◽  
Vol 1 (3) ◽  
pp. 145-153
Author(s):  
Jeremy M. Gosselin ◽  
Pascal Audet ◽  
Bill Fry ◽  
Emily Warren-Smith
Keyword(s):  
New Zealand ◽  
Stress State ◽  
Subduction Zone ◽  
Receiver Functions ◽  
Scattering Data ◽  
Eastern Coast ◽  
Plate Interface ◽  
Tectonic Plates ◽  
Megathrust Earthquakes ◽  
The North

Abstract The Hikurangi subduction zone (HSZ) is the collisional boundary between the Pacific and Australian tectonic plates along the eastern coast of the North Island of New Zealand. The region is believed to be capable of hosting large megathrust earthquakes and associated tsunamis. Recent studies observe a range of slip behavior along the plate interface, with a sharp contrast between locked and creeping parts of the megathrust along the margin. This work uses teleseismic scattering data (receiver functions [RFs]) recorded at 53 long-running seismograph stations on the North Island of New Zealand to constrain the structure and mechanical properties of the forearc in the HSZ. We observe directional variations in RF phases at P–S converted delay times (i.e., depths) associated with the overlying forearc crust and note a general correlation with spatial variations in plate coupling as well as other geophysical properties. Our results suggest differences in the nature of crustal deformation (and stress state) along the Hikurangi margin, with evidence of clockwise rotation and/or extension in the northern HSZ, where the overriding forearc crust is uncoupled from the subducting Pacific slab.

scholarly journals Adjoint tomography of the Hikurangi subduction zone and the North Island of New Zealand

2021 ◽  
Author(s):  
Bryant Chow
Keyword(s):  
New Zealand ◽  
Subduction Zone ◽  
East Coast ◽  
Plate Boundary ◽  
Velocity Model ◽  
Seismic Velocities ◽  
Low Velocity ◽  
Velocity Models ◽  
The North ◽  
Adjoint Tomography

<p><b>Seismic tomography is a powerful tool for understanding Earth structure. In New Zealand, velocity models derived using ray-based tomography have been used extensively to characterize the complex plate boundary between the Australian and Pacific plates. Advances in computational capabilities now allow us to improve these velocity models using adjoint tomography, an imaging method which minimizes differences between observed and simulated seismic waveforms. We undertake the first application of adjoint tomography in New Zealand to improve a ray-based New Zealand velocity model containing the Hikurangi subduction zone and the North Island of New Zealand.</b></p> <p>In support of this work we deployed the Broadband East Coast Network (BEACON), a temporary seismic network aimed at improving coverage of the New Zealand permanent network, along the east coast of the North Island. We concurrently develop an automated, open-source workflow for full-waveform inversion using spectral element and adjoint methods. We employ this tool to assess a candidate velocity model’s suitability for adjoint tomography. Using a 3D ray-based traveltime tomography model of New Zealand, we generate synthetic seismic waveforms for more than 10 000 source–receiver pairs and evaluate waveform misfits. We subsequently perform synthetic checkerboard inversions with a realistic New Zealand source–receiver distribution. Reasonable systematic time shifts and satisfactory checkerboard resolution in synthetic inversions indicate that the candidate model is appropriate as an initial model for adjoint tomography. This assessment also demonstrates the relative ease of use and reliability of the automated tools.</p> <p>We then undertake a large-scale adjoint tomography inversion for the North Island of New Zealand using up to 1 800 unique source–receiver pairs to fit waveforms with periods 4–30 s, relating to minimum waveform sensitivities on the order of 5 km. Overall, 60 geographically well-distributed earthquakes and as many as 88 broadband station locations are included. Using a nonlinear optimization algorithm, we undertake 28 model updates of Vp and Vs over six distinct inversion legs which progressively increase resolution. The total inversion incurred a computational cost of approximately 500 000 CPU-hours. The overall time shift between observed and synthetic seismograms is reduced, and updated velocities show as much as ±30% change with respect to initial values. A formal resolution analysis using point spread tests highlights that velocity changes are strongly resolved onland and directly offshore, at depths above 30 km, with low-amplitude changes (> 1%) observed down to 100 km depth. The most striking velocity changes coincide with areas related to the active Hikurangi subduction zone.</p> <p>We interpret the updated velocity model in terms of New Zealand tectonics and geology, and observe good agreement with known basement terranes, and major structural elements such as faults, sedimentary basins, broad-scale subduction related features. We recover increased spatial heterogeneity in seismic velocities along the strike of the Hikurangi subduction zone with respect to the initial model. Below the East Coast, we interpret two localized high-velocity anomalies as previously unidentified subducted seamounts. We corroborate this interpretation with other work, and discuss the implications of deeply subducted seamounts on slip behavior along the Hikurangi margin. In the Cook Strait we observe a low-velocity zone that we interpret as a deep sedimentary basin. Strong velocity gradients bounding this low-velocity zone support hypotheses of a structural boundary here separating the North and South Islands of New Zealand. In the central North Island, low-velocity anomalies are linked to surface geology, and we relate seismic velocities at depth to crustal magmatic activity below the Taupo Volcanic Zone.</p> <p>This new velocity model provides more accurate synthetic seismograms and additional constraints on enigmatic tectonic processes related to the North Island of New Zealand. Both the velocity model itself, and the underpinning methodological contributions, improve our ever-expanding understanding of the North Island of New Zealand, the Hikurangi subduction zone, and the broader Australian-Pacific plate boundary.</p>

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