scholarly journals Source Properties of Moderate-Magnitude Earthquakes Along the Alpine Fault, New Zealand

2021 ◽  
Author(s):  
Ilma Del Carmen Juarez Garfias
Keyword(s):  
New Zealand ◽  
Stress Drop ◽  
Boundary Zone ◽  
The South ◽  
S Waves ◽  
The North ◽  
Alpine Fault ◽  
Central Segment ◽  
Stress Drops ◽  
Moderate Magnitude

<p><b>The Alpine Fault is a major active continental transform fault that is late in its typical cycle of large earthquakes. Extensive paleoseismic research has revealed that the central segment of the Alpine Fault ruptures in M7+ earthquakes every 291±23 years and last ruptured in 1717 AD. The paleoseismic results also reveal that some places along the fault, which coincide with pronounced along-strike changes in fault characteristics, act as conditional barriers to rupture. The geometry, seismicity rates and geology of the Alpine Fault change along three principal segments (North Westland, Central and South Westland segments) but it is unclear whether source properties (e.g. stress drop) of near-fault seismicity also vary between those fault segments, and whether these properties have some influence on conditional segmentation of the Alpine Faultduring large earthquake rupture.</b></p> <p>To examine whether source properties of earthquakes can influence or elucidate the conditional segmentation of Alpine Fault earthquakes, we have computed stress drops of moderate-magnitude earthquakes occurring on and close to the Alpine Fault. We use an empirical Green’s function (EGF) approach and require each EGF earthquake to be highly correlated (cross-correlation ≥0.8) with its respective mainshock. We use data from dense, temporary seismometer networks, including DWARFS (Dense WestlandArrays Researching Fault Segmentation), a new two-part network designed to constrain seismogenic behaviour near key transitional boundaries. Our results investigate the spatial variability of these source properties along the length of the Alpine Fault, focusing on whether earthquakes at the rupture segment boundaries behave differently to those in the middle of previously identified rupture segments.</p> <p>We analyse individual P- and S-wave measurements of corner frequency and stress drop for 95 earthquakes close to (within 5 km) and on the Alpine Fault. Overall, the calculated stress drops range between 1–352 MPa and show good agreement with other studies both within New Zealand and worldwide. The stress drop values obtained for the three Alpine segment are: 1–143 MPa (median values of 8 and 9 MPa for P- and S-waves, respectively) for the South Westland/Central segment boundary zone, 2–309 MPa (median values of 17 and 39 MPa for P- and S-waves, respectively) for the Central segment and 1–352 MPa (median values of 15 and 19 MPa for P- and S-waves, respectively) for the North Westland/Central segment boundary zone. There are no marked differences in stress drop values along the North Westland and Central segments, but those values are slightly higher than along the South Westland segment.</p> <p>This may indicate a bigger difference in fault geometry, slip and seismicity rate compare with other segments, or that the South Westland segment is weaker than the other segments. We see no clear dependence of stress drop values on depth, magnitude or focal mechanism.</p>

scholarly journals Source Properties of Moderate-Magnitude Earthquakes Along the Alpine Fault, New Zealand

2021 ◽  
Author(s):  
◽  
Ilma Del Carmen Juarez Garfias
Keyword(s):  
New Zealand ◽  
Stress Drop ◽  
Boundary Zone ◽  
The South ◽  
S Waves ◽  
The North ◽  
Alpine Fault ◽  
Central Segment ◽  
Stress Drops ◽  
Moderate Magnitude

<p><b>The Alpine Fault is a major active continental transform fault that is late in its typical cycle of large earthquakes. Extensive paleoseismic research has revealed that the central segment of the Alpine Fault ruptures in M7+ earthquakes every 291±23 years and last ruptured in 1717 AD. The paleoseismic results also reveal that some places along the fault, which coincide with pronounced along-strike changes in fault characteristics, act as conditional barriers to rupture. The geometry, seismicity rates and geology of the Alpine Fault change along three principal segments (North Westland, Central and South Westland segments) but it is unclear whether source properties (e.g. stress drop) of near-fault seismicity also vary between those fault segments, and whether these properties have some influence on conditional segmentation of the Alpine Faultduring large earthquake rupture.</b></p> <p>To examine whether source properties of earthquakes can influence or elucidate the conditional segmentation of Alpine Fault earthquakes, we have computed stress drops of moderate-magnitude earthquakes occurring on and close to the Alpine Fault. We use an empirical Green’s function (EGF) approach and require each EGF earthquake to be highly correlated (cross-correlation ≥0.8) with its respective mainshock. We use data from dense, temporary seismometer networks, including DWARFS (Dense WestlandArrays Researching Fault Segmentation), a new two-part network designed to constrain seismogenic behaviour near key transitional boundaries. Our results investigate the spatial variability of these source properties along the length of the Alpine Fault, focusing on whether earthquakes at the rupture segment boundaries behave differently to those in the middle of previously identified rupture segments.</p> <p>We analyse individual P- and S-wave measurements of corner frequency and stress drop for 95 earthquakes close to (within 5 km) and on the Alpine Fault. Overall, the calculated stress drops range between 1–352 MPa and show good agreement with other studies both within New Zealand and worldwide. The stress drop values obtained for the three Alpine segment are: 1–143 MPa (median values of 8 and 9 MPa for P- and S-waves, respectively) for the South Westland/Central segment boundary zone, 2–309 MPa (median values of 17 and 39 MPa for P- and S-waves, respectively) for the Central segment and 1–352 MPa (median values of 15 and 19 MPa for P- and S-waves, respectively) for the North Westland/Central segment boundary zone. There are no marked differences in stress drop values along the North Westland and Central segments, but those values are slightly higher than along the South Westland segment.</p> <p>This may indicate a bigger difference in fault geometry, slip and seismicity rate compare with other segments, or that the South Westland segment is weaker than the other segments. We see no clear dependence of stress drop values on depth, magnitude or focal mechanism.</p>

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.

scholarly journals Ecological impact and spread of an invasive paper wasp in New Zealand (Hymenoptera: Vespidae)

2021 ◽  
Author(s):  
Matthew Howse
Keyword(s):  
At Risk ◽  
Invasive Species ◽  
New Zealand ◽  
Ecological Impact ◽  
Diet Analysis ◽  
Paper Wasp ◽  
Gut Contents ◽  
Suitable Habitat ◽  
The South ◽  
The North

<p><b>Social wasps are considered among the most successful and impactful invasive species in the world. One species, Polistes dominula has spread from its native Mediterranean range to every continent except Antarctica. This wasp reached New Zealand in the last decade where it has established in the north of the South Island, however, reports of its presence are increasing throughout the country. Due to its recent arrival in New Zealand, little is known about where this species is likely to establish or what impacts it may have on local insect communities. In this thesis, I conducted two studies to investigate these questions, providing valuable information that may inform future management of this invasive species. </b></p><p>In chapter 2, I used two bioclimatic modelling methods to predict areas of suitable habitat across four regions in the southern hemisphere. These models were informed by global temperature and precipitation data as well as global distribution occurrence data of P. dominula. These data were used to estimate conditions most highly correlated with the presence of this wasp. The models identified large areas across the target regions that were climatically suitable for the establishment of P. dominula. Many of these areas are not known to currently contain populations of this species, representing habitat potentially vulnerable to further invasion by P. dominula. Areas across South America, South Africa and Australia were predicted to be climatically suitable. In New Zealand, much of the North Island and eastern parts of the South Island were predicted to be suitable habitat for this wasp. These results suggest that P. dominula could potentially establish across more of the country and expand its invaded range. Information provided by these models may guide conservation and biosecurity management by highlighting key areas where prevention and mitigation should be prioritized. </p><p>In chapter 3, I used molecular diet analysis to investigate the range of prey being utilised by P. dominula in New Zealand. Using DNA barcoding, larval gut contents of P. dominula and another closely related species, Polistes chinensis, were analysed to identify what species were present in the diet of both wasps. Butterflies and moths (Lepidoptera) were found to be the most highly represented order in both species’ diets. True bugs (Hemiptera) and flies (Diptera) were also abundant. Both wasps were shown to consume a range of native and introduced species including a number of agricultural pests. P. dominula was found to utilise a wider range of prey than P. chinensis. This more diverse prey range, combined with known differences in nesting behaviour, suggest that P. dominula may represent a more significant threat to invertebrate diversity than the already well-established P. chinensis. These results may inform conservation and biosecurity managers on which species are most at risk where this new invasive wasp becomes established. </p><p>This thesis provides insights into the potential impacts of a new invasive species to New Zealand. Both chapters represent the first time that these methods have been used to study P. dominula. This work highlights the need for continued monitoring of wasp populations throughout New Zealand, especially in regions highlighted as vulnerable to P. dominula establishment. We also suggest the need to prioritise the conservation of ‘at-risk’ species in coastal and human-altered habitats. Increased public engagement through the citizen-science initiatives should be encouraged while more research into management and control methods is recommended.</p>

The discovery of a new sedimentary basin: offshore Raukumara, East Coast, North Island, New Zealand

2008 ◽  
Vol 48 (1) ◽  
pp. 53 ◽  
Author(s):  
Chris Uruski ◽  
Callum Kennedy ◽  
Rupert Sutherland ◽  
Vaughan Stagpoole ◽  
Stuart Henrys
Keyword(s):  
New Zealand ◽  
Oil And Gas ◽  
East Coast ◽  
Plate Boundary ◽  
Source Rocks ◽  
Fault System ◽  
Northern Coast ◽  
The South ◽  
Petroleum Potential ◽  
The North

The East Coast of North Island, New Zealand, is the site of subduction of the Pacific below the Australian plate, and, consequently, much of the basin is highly deformed. An exception is the Raukumara Sub-basin, which forms the northern end of the East Coast Basin and is relatively undeformed. It occupies a marine plain that extends to the north-northeast from the northern coast of the Raukumara Peninsula, reaching water depths of about 3,000 m, although much of the sub-basin lies within the 2,000 m isobath. The sub-basin is about 100 km across and has a roughly triangular plan, bounded by an east-west fault system in the south. It extends about 300 km to the northeast and is bounded to the east by the East Cape subduction ridge and to the west by the volcanic Kermadec Ridge. The northern seismic lines reveal a thickness of around 8 km increasing to 12–13 km in the south. Its stratigraphy consists of a fairly uniformly bedded basal section and an upper, more variable unit separated by a wedge of chaotically bedded material. In the absence of direct evidence from wells and samples, analogies are drawn with onshore geology, where older marine Cretaceous and Paleogene units are separated from a Neogene succession by an allochthonous series of thrust slices emplaced around the time of initiation of the modern plate boundary. The Raukumara Sub-basin is not easily classified. Its location is apparently that of a fore-arc basin along an ocean-to-ocean collision zone, although its sedimentary fill must have been derived chiefly from erosion of the New Zealand land mass. Its relative lack of deformation introduces questions about basin formation and petroleum potential. Although no commercial discoveries have been made in the East Coast Basin, known source rocks are of marine origin and are commonly oil prone, so there is good potential for oil as well as gas in the basin. New seismic data confirm the extent of the sub-basin and its considerable sedimentary thickness. The presence of potential trapping structures and direct hydrocarbon indicators suggest that the Raukumara Sub-basin may contain large volumes of oil and gas.

I.—The Glacial Controversy in New Zealand

1917 ◽  
Vol 4 (6) ◽  
pp. 241-245 ◽  
Author(s):  
C. T. Trechmann
Keyword(s):  
New Zealand ◽  
Ice Sheet ◽  
Pleistocene Glaciation ◽  
The South ◽  
The North

The controversy which has arisen in recent years in New Zealand regarding the problem of the Pleistocene glaciation of that country resolves itself into the two following main questions:—1. Was there any glaciation in the North Island?2. Was there an ice-sheet covering the South Island?

Ocean Cruising: A Sailing Subculture

1992 ◽  
Vol 40 (2) ◽  
pp. 319-343 ◽  
Author(s):  
Jim Macbeth
Keyword(s):  
New Zealand ◽  
North Atlantic ◽  
South Pacific ◽  
The South ◽  
Fringing Reef ◽  
The North ◽  
Hurricane Season ◽  
The North Atlantic ◽  
One Year

Just after dawn, an English couple in their 30's haul up their anchor and motor across the stillness of Suva harbour. The hurricane season is approaching and they are embarking on the 2–3 week trip to Bay of Islands New Zealand for the southern summer. Three months earlier, as their yacht lay aground on the fringing reef of uninhabited Suvarov atoll, they wondered if they'd ever reach New Zealand. But, with the help of other cruisers and lucky tides their steel 36 footer was clear and safe in under 24 hours. What was to be a one year trip around the north Atlantic was now happily way off course in the South Pacific and likely to remain so for some time. That is just a glimpse of one small aspect of ocean cruising, the subculture of interest here. However, throughout the paper the ethnography of cruising is developed further. A model is proposed to show how individuals come to share the subculture ideology and then to participate in the lifestyle. Subsequently, 1 will place ocean cruising in the context of subculture theory by expanding the ethnography and relating cruising to other subcultures.

scholarly journals Regional Variation in New Zealand English: the Taranaki Sing-Song Accent

2021 ◽  
Author(s):  
◽  
Helen Ainsworth
Keyword(s):  
Social Network ◽  
New Zealand ◽  
Regional Variation ◽  
Regional Differences ◽  
The Elderly ◽  
The South ◽  
The North ◽  
Pitch Direction ◽  
Auditory Analysis ◽  
Pitch Movement

<p>Although lay people confidently assert the existence of regional varieties of New Zealand English, linguists have produced very little evidence to support such claims. There are vocabulary items special to, or favoured by, the people of Southland and the West Coast of the South Island; there are traces of non-prevocalic /r/in Southland and Otago; and there are regional differences in the playground language of New Zealand school children. Attempts to identify further differences between regions have generally not been successful. In most cases linguistic evidence has pointed to either social class or ethnic variation, but not to regional variation. Nevertheless, many New Zealanders assert that a Taranaki variety of New Zealand English exists. This study was designed to test the validity of the claim by comparing samples of New Zealand English from Taranaki with samples from Wellington. The Taranaki sample included speakers from New Plymouth (population 50,000) and the South Taranaki dairy farming community. The Wellington sample was drawn from the Greater Wellington region extending from Porirua in the north to suburbs on the southern coast of the city. Interviewees were located by the social network approach, otherwise known as the 'friend of a friend' approach advocated by Lesley Milroy (1980, 1987a). An index of rural orientation was devised to indicate the degree to which a speaker was oriented towards town or country. This proved helpful in distinguishing between genuinely regional differences, and rural versus urban differences. Factors of gender and age were also considered. It has been claimed that Taranaki English has a 'sing-song' quality, suggesting that an investigation of the intonation of Taranaki speakers would be worthwhile. Comparing features of the intonation of a Taranaki sample with a Wellington sample, this thesis attempts to isolate and measure what contributes to the 'sing-song' perception of Taranaki English. 'Singsong' in this context was taken to mean that the speaker had dynamic pitch; in other words their speech was characterised by a lot of movement up and down in pitch. Auditory analysis of speech samples was undertaken, and intonation features were derived from that analysis. Averaging the number of times a speaker changed pitch direction in each intonation group and then in each accent unit provided global measures of changes in pitch direction. Analysis of nuclear accents gave an indication of whether speakers favoured tunes which were characterised by pitch movement. And analysis of the manner in which accents were approached, whether with a boosted step up in pitch, or with a more standard onset, provided a narrower focus on the amount of pitch movement present. Results indicated that, in general, most Taranaki speakers in the sample showed more pitch dynamism than the Wellingtonians; for some features the males showed more pitch dynamism than the females; and, overall, the elderly speakers showed more pitch dynamism than the younger speakers. There were, however, important exceptions to these generalisations. Factors of Location, Gander and Age interacted significantly for all but one of the features examined and there were clear indications that intonational patterns are undergoing change in both regions studied. Explanations for the exceptional cases are explored in the thesis, and sociolinguistic, social network and geolinguistic theories provide possible clues as to the sources of the differences. Evidence of differences in the degree of pitch dynamism present in the intonation of the Taranaki and Wellington speakers supports claims about regional variation in New Zealand English intonation, but it does not in itself prove the existence of a uniquely Taranaki or a uniquely Wellington way of speaking English.</p>

scholarly journals Commensal Rodents in 19th Century Australasia: Diversity, Invasion Routes and the China Connection

2021 ◽  
Author(s):  
Andrew James Veale ◽  
Carolyn King ◽  
Wayne Johnson ◽  
Lara Shepherd
Keyword(s):  
Genetic Diversity ◽  
New Zealand ◽  
Dna Sequences ◽  
Archaeological Site ◽  
House Mice ◽  
Mus Musculus Domesticus ◽  
The South ◽  
The North ◽  
Founding Population ◽  
Norway Rats

Abstract The present genetic diversity of commensal rodent populations is often used to inform the invasion histories of these species, and as a proxy for historical events relating to the movement of people and goods. These studies assume that modern genetic diversity generally reflects early colonising events. We investigate this idea by sequencing the mitochondrial DNA of rodent bones found in a 19th-century archaeological site in The Rocks area of Sydney, Australia, the location of the first historical European port. We identified 19th-century bones from two species, Rattus norvegicus and Mus musculus domesticus. We found six genetic haplotypes in the 39 Norway rats, showing either multiple early introductions or a diverse initial founding population. One of them was identical with Norhap01 common in the North Island of New Zealand, but none was like the haplotype Norhap02 found throughout the South Island. We found three haplotypes in seven house mice, all belonging to the dominant subspecies established in Australia, M.m. domesticus. There was no evidence for M. m. castaneus or M. m. musculus having established there. We had few modern R. norvegicus and M. musculus DNA sequences from Sydney, but those we had did tentatively support the hypotheses that (1) modern samples can represent at least a preliminary estimate of historical diversities and origins, and (2) Asian haplotypes of both Norway rats and of house mice reached the South Island of New Zealand early in colonial times direct from China rather than through Port Jackson.

scholarly journals Chemical data on some rock-forming minerals from high-grade gneisses, amphibolites and anorthosites from the Fiskenæsset area

1971 ◽  
Vol 35 ◽  
pp. 22-23
Author(s):  
T Frisch
Keyword(s):  
Rock Type ◽  
Amphibolite Facies ◽  
Chemical Data ◽  
High Grade ◽  
Boundary Zone ◽  
Areal Extent ◽  
Common Occurrence ◽  
The South ◽  
The West ◽  
The North

The area mapped by the writer is situated to the west of Fiskenæsset and lies in the boundary zone between granulite and amphibolite facies rocks (see Kalsbeek, this report). In the north a creamy- to pink-weathering gneiss, commonly containing hypersthene and biotite is the chief rock type. In the south small-folded, pale-grey weathering biotite-hornblende gneisses are predominant. Amphibolite is of common occurrence in layers, pods and agmatite. The areal extent of the anorthosite-pyribolite complex as previously outlined by reconnaissance mapping (Ghisler & Windley, 1967) was confirmed in general but modified in detail. Additional occurrences of rocks belonging to the complex were found.

Sign in / Sign up

Export Citation Format

Share Document