An automated workflow for adjoint tomography—waveform misfits and synthetic inversions for the North Island, New Zealand

2020 ◽  
Vol 223 (3) ◽  
pp. 1461-1480
Author(s):  
Bryant Chow ◽  
Yoshihiro Kaneko ◽  
Carl Tape ◽  
Ryan Modrak ◽  
John Townend
Keyword(s):  
New Zealand ◽  
Large Scale ◽  
Cross Correlation ◽  
Phase Measurement ◽  
Workflow Management ◽  
Velocity Model ◽  
Spectral Element ◽  
Seismic Inversion ◽  
Ease Of Use ◽  
The North

SUMMARY We develop and verify an automated workflow for full-waveform tomography based on spectral element and adjoint methods. We choose the North Island, New Zealand as a study area because of its high seismicity, extensive seismic network, and the availability of a candidate ray tomography starting model. To assess the accuracy of this model, we simulated 250 regional earthquakes using a spectral element solver, and compared the resulting synthetics with recorded waveforms. In a 10–30 s passband, reasonable cross-correlation phase and amplitude misfits exist between data and synthetics, whereas at 2–30 s, waveform misalignment is severe enough that meaningful cross-correlation measurements are no longer possible. To improve the velocity model at these short periods, we created an automated inversion framework based on existing tools for signal processing, phase measurement, nonlinear optimization, and workflow management. To verify the inversion framework, we performed a realistic synthetic inversion for 3-D checkerboard structure and analyzed model recovery, misfit reduction, and waveform improvement. The results of this analysis show that the source–receiver distribution within the chosen domain is capable of resolving velocity anomalies in regions of sufficient data coverage, and of magnitudes comparable to those expected in a real seismic inversion. Along with this finding, the relative ease of use and reliability of the workflow motivates future efforts targeting a high-resolution (2–30 s), large-scale (>50 000 measurements) seismic inversion for the North Island. Updated models from such an inversion are expected to improve ground motion predictions, constrain complex velocity structures, and advance understanding of New Zealand tectonics.

scholarly journals Mapping Stress and Structure From Subducting Slab to Magmatic Rift: Crustal Seismic Anisotropy of the North Island, New Zealand

2020 ◽  
Author(s):  
Finnigan Illsley-Kemp ◽  
Martha Savage ◽  
Colin Wilson ◽  
S Bannister
Keyword(s):  
New Zealand ◽  
Stress Field ◽  
Large Scale ◽  
Seismic Anisotropy ◽  
Taupo Volcanic Zone ◽  
Volcanic Zone ◽  
The North ◽  
Magma Reservoirs ◽  
Tectonic Forces ◽  
Subducting Slab

© 2019. American Geophysical Union. All Rights Reserved. We use crustal seismic anisotropy measurements in the North Island, New Zealand, to examine structures and stress within the Taupō Volcanic Zone, the Taranaki Volcanic Lineament, the subducting Hikurangi slab, and the Hikurangi forearc. Results in the Taranaki region are consistent with NW-SE oriented extension yet suggest that the Taranaki volcanic lineament may be controlled by a deep-rooted, inherited crustal structure. In the central Taupō Volcanic Zone anisotropy fast orientations are predominantly controlled by continental rifting. However at Taupō and Okataina volcanoes, fast orientations are highly variable and radial to the calderas suggesting the influence of magma reservoirs in the seismogenic crust (≤15 km depth). The subducting Hikurangi slab has a predominant trench-parallel fast orientation, reflecting the pervasive presence of plate-bending faults, yet changing orientations at depths ≥120 km beneath the central North Island may be relics from previous subduction configurations. Finally, results from the southern Hikurangi forearc show that the orientation of stresses there is consistent with those in the underlying subducting slab. In contrast, the northern Hikurangi forearc is pervasively fractured and is undergoing E-W compression, oblique to the stress field in the subducting slab. The north-south variation in fore-arc stress is likely related to differing subduction-interface coupling. Across the varying tectonic regimes of the North Island our study highlights that large-scale tectonic forces tend to dictate the orientation of stress and structures within the crust, although more localized features (plate coupling, magma reservoirs, and inherited crustal structures) can strongly influence surface magmatism and the crustal stress field.

Causes of Late Twentieth-Century Trends in New Zealand Precipitation

2009 ◽  
Vol 22 (1) ◽  
pp. 3-19 ◽  
Author(s):  
Caroline C. Ummenhofer ◽  
Alexander Sen Gupta ◽  
Matthew H. England
Keyword(s):  
Twentieth Century ◽  
New Zealand ◽  
Southern Hemisphere ◽  
Large Scale ◽  
Austral Summer ◽  
Climate Modes ◽  
The North ◽  
Late Twentieth ◽  
Late Twentieth Century ◽  
Large Scale Atmospheric Circulation

Abstract Late twentieth-century trends in New Zealand precipitation are examined using observations and reanalysis data for the period 1979–2006. One of the aims of this study is to investigate the link between these trends and recent changes in the large-scale atmospheric circulation in the Southern Hemisphere. The contributions from changes in Southern Hemisphere climate modes, particularly the El Niño–Southern Oscillation (ENSO) and the southern annular mode (SAM), are quantified for the austral summer season, December–February (DJF). Increasingly drier conditions over much of New Zealand can be partially explained by the SAM and ENSO. Especially over wide parts of the North Island and western regions of the South Island, the SAM potentially contributes up to 80% and 20%–50% to the overall decline in DJF precipitation, respectively. Over the North Island, the contribution of the SAM and ENSO to precipitation trends is of the same sign. In contrast, over the southwest of the South Island the two climate modes act in the opposite sense, though the effect of the SAM seems to dominate there during austral summer. The leading modes of variability in summertime precipitation over New Zealand are linked to the large-scale atmospheric circulation. The two dominant modes, explaining 64% and 9% of the overall DJF precipitation variability respectively, can be understood as local manifestations of the large-scale climate variability associated with the SAM and ENSO.

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>

Large-scale trapping of sheep blowflies in the northern North Island of New Zealand using insecticide-free traps

1995 ◽  
Vol 35 (6) ◽  
pp. 699 ◽  
Author(s):  
JJ Dymock ◽  
SA Forgie
Keyword(s):  
New Zealand ◽  
Large Scale ◽  
Lucilia Cuprina ◽  
Trap Site ◽  
Mixed Farming ◽  
The North ◽  
Trap Colour

Large-scale trapping of sheep blowflies (Diptera: Calliphoridae) was undertaken on a mixed farming property in the north of the North Island of New Zealand over 3 consecutive summers. Traps were placed at a density of 1 trap110 ha and baited with fresh sheep offal every 2 weeks. No insecticide was used in the 150-L traps. The most effective bait trialled was sheep offal <2 weeks old. There was no significant effect of trap colour or trap site on the number of blowflies caught. A 95% decline in the principal flystike blowfly, Lucilia cuprina, was recorded. Flystrike incidence at the site was low during the study so that the effect of trapping on sheep myiasis could not be determined.

scholarly journals Validation of the saliva-based H. pylori test, HeliSAL™, and its use in prevalence surveys

2001 ◽  
Vol 126 (2) ◽  
pp. 191-196 ◽  
Author(s):  
M. COCKBURN ◽  
J. COLLETT ◽  
B. COX
Keyword(s):  
New Zealand ◽  
Clinical Diagnosis ◽  
Clinical Setting ◽  
Gold Standard ◽  
Large Scale ◽  
Population Based ◽  
Ease Of Use ◽  
Non Invasive ◽  
Test Sensitivity ◽  
H Pylori

The saliva-based H. pylori test, HeliSAL™, is insufficiently accurate for use in the clinical setting. However, its ease of use and non-invasiveness make it attractive for population-based studies of the epidemiology of H. pylori. We validated HeliSAL™, and comment here on its usefulness in prevalence surveys. One hundred and ninety-six patients receiving endoscopy at a clinic in New Zealand provided saliva samples for H. pylori assessment, which were compared to CLOtest (Delta West Pty Ltd, Western Australia) as a gold standard measure. Nineteen percent were truly H. pylori positive, 41 % were positive according to HeliSAL™. Test sensitivity was 74 % and specificity was 67 %. While HeliSAL™ is not well suited for the clinical diagnosis of H. pylori infection, it may be useful for large-scale prevalence surveys because, provided it is validated locally, mathematical adjustment can be made for misclassification. Being inexpensive, non-invasive, and easily stored and handled, HeliSAL™ may be a valuable tool for studies of the epidemiology of H. pylori.

scholarly journals Mapping Stress and Structure From Subducting Slab to Magmatic Rift: Crustal Seismic Anisotropy of the North Island, New Zealand

2020 ◽  
Author(s):  
Finnigan Illsley-Kemp ◽  
Martha Savage ◽  
Colin Wilson ◽  
S Bannister
Keyword(s):  
New Zealand ◽  
Stress Field ◽  
Large Scale ◽  
Seismic Anisotropy ◽  
Taupo Volcanic Zone ◽  
Volcanic Zone ◽  
The North ◽  
Magma Reservoirs ◽  
Tectonic Forces ◽  
Subducting Slab

© 2019. American Geophysical Union. All Rights Reserved. We use crustal seismic anisotropy measurements in the North Island, New Zealand, to examine structures and stress within the Taupō Volcanic Zone, the Taranaki Volcanic Lineament, the subducting Hikurangi slab, and the Hikurangi forearc. Results in the Taranaki region are consistent with NW-SE oriented extension yet suggest that the Taranaki volcanic lineament may be controlled by a deep-rooted, inherited crustal structure. In the central Taupō Volcanic Zone anisotropy fast orientations are predominantly controlled by continental rifting. However at Taupō and Okataina volcanoes, fast orientations are highly variable and radial to the calderas suggesting the influence of magma reservoirs in the seismogenic crust (≤15 km depth). The subducting Hikurangi slab has a predominant trench-parallel fast orientation, reflecting the pervasive presence of plate-bending faults, yet changing orientations at depths ≥120 km beneath the central North Island may be relics from previous subduction configurations. Finally, results from the southern Hikurangi forearc show that the orientation of stresses there is consistent with those in the underlying subducting slab. In contrast, the northern Hikurangi forearc is pervasively fractured and is undergoing E-W compression, oblique to the stress field in the subducting slab. The north-south variation in fore-arc stress is likely related to differing subduction-interface coupling. Across the varying tectonic regimes of the North Island our study highlights that large-scale tectonic forces tend to dictate the orientation of stress and structures within the crust, although more localized features (plate coupling, magma reservoirs, and inherited crustal structures) can strongly influence surface magmatism and the crustal stress field.

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>

Why Has There Been No People’s Power Rebellion in North Korea?

2018 ◽  
pp. 1-34
Author(s):  
Andrew Jackson
Keyword(s):  
Rural Areas ◽  
North Korea ◽  
Large Scale ◽  
Political Elite ◽  
Information Control ◽  
Al Jazeera ◽  
The North ◽  
New Information ◽  
Effective System ◽  
The Right

One scenario put forward by researchers, political commentators and journalists for the collapse of North Korea has been a People’s Power (or popular) rebellion. This paper analyses why no popular rebellion has occurred in the DPRK under Kim Jong Un. It challenges the assumption that popular rebellion would happen because of widespread anger caused by a greater awareness of superior economic conditions outside the DPRK. Using Jack Goldstone’s theoretical expla-nations for the outbreak of popular rebellion, and comparisons with the 1989 Romanian and 2010–11 Tunisian transitions, this paper argues that marketi-zation has led to a loosening of state ideological control and to an influx of infor-mation about conditions in the outside world. However, unlike the Tunisian transitions—in which a new information context shaped by social media, the Al-Jazeera network and an experience of protest helped create a sense of pan-Arab solidarity amongst Tunisians resisting their government—there has been no similar ideology unifying North Koreans against their regime. There is evidence of discontent in market unrest in the DPRK, although protests between 2011 and the present have mostly been in defense of the right of people to support themselves through private trade. North Koreans believe this right has been guaranteed, or at least tacitly condoned, by the Kim Jong Un government. There has not been any large-scale explosion of popular anger because the state has not attempted to crush market activities outright under Kim Jong Un. There are other reasons why no popular rebellion has occurred in the North. Unlike Tunisia, the DPRK lacks a dissident political elite capable of leading an opposition movement, and unlike Romania, the DPRK authorities have shown some flexibility in their anti-dissent strategies, taking a more tolerant approach to protests against economic issues. Reduced levels of violence during periods of unrest and an effective system of information control may have helped restrict the expansion of unrest beyond rural areas.

Information And Map-Made Control With The Functions Of Business Analytics For Urban Management

2019 ◽  
pp. 72-78
Keyword(s):  
Large Scale ◽  
Information Support ◽  
Urban Management ◽  
Business Analytics ◽  
Administrative District ◽  
The North ◽  
Model Of Management ◽  
Complex Development ◽  
Coordination System ◽  
Key Aspects

The key aspects of the process of designing and developing an information and cartographic control tool with business analytics functions for the municipal level of urban management are considered. The review of functionality of the developed tool is given. Examples of its use for the analysis and monitoring of implementation of the program of complex development of territories are given. The importance of application of information support of management and coordination at all levels of management as an integral part of the basic model of management and coordination system of large-scale urban projects of dispersed construction is proved. Information and map-made tool with business intelligence functions was used and was highly appreciated in the preparation of information-analytical and presentation materials of the North-Eastern Administrative District of Moscow. Its use made it possible to significantly optimize the list of activities of the program of integrated development of territories, their priority and timing.

Partnerships Generate Co-Benefits in Agricultural Stream Restoration (Canterbury, New Zealand)

2020 ◽  
Vol 4 (1) ◽  
Author(s):  
Catherine M. Febria ◽  
Maggie Bayfield ◽  
Kathryn E. Collins ◽  
Hayley S. Devlin ◽  
Brandon C. Goeller ◽  
...  
Keyword(s):  
New Zealand ◽  
Large Scale ◽  
Agricultural Land ◽  
Indigenous Rights ◽  
Freshwater Ecosystem ◽  
Reduced Pressure ◽  
Ecosystem Integrity ◽  
Riparian Management ◽  
Scale Change ◽  
Large Scale Change

In Aotearoa New Zealand, agricultural land-use intensification and decline in freshwater ecosystem integrity pose complex challenges for science and society. Despite riparian management programmes across the country, there is frustration over a lack in widespread uptake, upfront financial costs, possible loss in income, obstructive legislation and delays in ecological recovery. Thus, social, economic and institutional barriers exist when implementing and assessing agricultural freshwater restoration. Partnerships are essential to overcome such barriers by identifying and promoting co-benefits that result in amplifying individual efforts among stakeholder groups into coordinated, large-scale change. Here, we describe how initial progress by a sole farming family at the Silverstream in the Canterbury region, South Island, New Zealand, was used as a catalyst for change by the Canterbury Waterway Rehabilitation Experiment, a university-led restoration research project. Partners included farmers, researchers, government, industry, treaty partners (Indigenous rights-holders) and practitioners. Local capacity and capability was strengthened with practitioner groups, schools and the wider community. With partnerships in place, co-benefits included lowered costs involved with large-scale actions (e.g., earth moving), reduced pressure on individual farmers to undertake large-scale change (e.g., increased participation and engagement), while also legitimising the social contracts for farmers, scientists, government and industry to engage in farming and freshwater management. We describe contributions and benefits generated from the project and describe iterative actions that together built trust, leveraged and aligned opportunities. These actions were scaled from a single farm to multiple catchments nationally.

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