scholarly journals A model for the attenuation of peak ground acceleration in New Zealand earthquakes based on seismograph and accelerograph data

1999 ◽  
Vol 32 (4) ◽  
pp. 193-220 ◽  
Author(s):  
W. J. Cousins ◽  
J. X. Zhao ◽  
N. D. Perrin
Keyword(s):  
New Zealand ◽  
Peak Ground Acceleration ◽  
Strong Motion ◽  
Taupo Volcanic Zone ◽  
Weak Rock ◽  
Volcanic Zone ◽  
Ground Acceleration ◽  
High Attenuation ◽  
The North ◽  
Strong Rock

A combination of weak-motion velocity data from seismographs and strong-motion acceleration data from accelerographs has been used to model the attenuation of peak ground acceleration (PGA) in New Zealand earthquakes. The resulting model extends the PGA attenuation model of Zhao, Dowrick and McVerry [30] to include the variability of rock strength, and also describes the unusually high attenuation in the volcanic zone of the North Island of New Zealand. Strong-rock sites were found to experience lower PGAs than either weak rock or soil sites for magnitudes below Mw 7, and the apparent degree of amplification on going from strong rock to weak rock or soil decreased as the magnitude increased from Mw 5 to Mw 7. At magnitude 7 the PGAs were very similar for all site classes for source distances up to 100 km. When extrapolated to magnitudes beyond the maximum of the data, Mw 7.4, the model predicted that PGAs for strong rock sites were greater than for weak rock or soil sites. The so-called "whole Taupo Volcanic Zone" was found to provide a good boundary for the zone of high attenuation in the volcanic region of the North Island. The high attenuation was successfully modelled as a simple function of the length of travel path through the zone of high attenuation. Over the effective maximum volcanic path length of about 70 km the extra attenuation resulted in a factor of ten reduction in PGA compared with non-volcanic paths of the same length.

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.

A microearthquake survey at the Ngawha geothermal field, New Zealand

Geophysics ◽  
1981 ◽  
Vol 46 (10) ◽  
pp. 1467-1468 ◽  
Author(s):  
Russell Robinson
Keyword(s):  
New Zealand ◽  
Hot Springs ◽  
Geothermal Field ◽  
Hot Water ◽  
Taupo Volcanic Zone ◽  
Thermal Activity ◽  
Volcanic Zone ◽  
Depth Level ◽  
Geothermal Exploration ◽  
The North

A twenty day microearthquake survey of the Ngawha geothermal field, New Zealand, was undertaken in order to establish the level of preproduction seismicity and to test the usefulness of such surveys in geothermal exploration. The Ngawha geothermal field, in the far northwest of the North Island (Northland) is associated with a region of Quaternary basaltic volcanism. It is not a part of the much more extensive Taupo volcanic zone in the central North Island, site of the well‐known Wairakei geothermal field, among others. Although surface thermal activity at Ngawha is limited to a few relatively small hot springs, resistivity surveys have outlined a [Formula: see text] area of hot water at the 1-km depth level (Macdonald et al. , 1977). Test bores to that depth have encountered temperatures of up to 250 °C within Mesozoic graywacke. Overlying the graywacke is about 500 m of Cenozoic claystone and siltstone which forms an impermeable cap.

Taxonomic fidelity of silicified filamentous microbes from hot-spring systems in the Taupo Volcanic Zone, North Island, New Zealand

2003 ◽  
Vol 94 (4) ◽  
pp. 475-483 ◽  
Author(s):  
Brian Jones ◽  
Robin W. Renaut ◽  
Michael R. Rosen
Keyword(s):  
New Zealand ◽  
Hot Springs ◽  
Hot Spring ◽  
Morphological Characteristics ◽  
Colony Morphology ◽  
Taupo Volcanic Zone ◽  
Volcanic Zone ◽  
The North ◽  
Preservation Potential ◽  
Physical Changes

ABSTRACTModern, silica-precipitating hot springs, like those found in the Taupo Volcanic Zone (TVZ) on the North Island of New Zealand, are natural laboratories for assessing microbial silicification. Many of the silicified microbes found in the siliceous sinters of these spring systems seem to be life-like replicas of the original microbes. Such preservation reflects the fact that many of the microbes are replaced and encrusted by opal-A before they are destroyed by desiccation and decay. The taxonomic fidelity of these silicified microbes depends on the preservation potential of those features which are needed to identify them. For example, identification of extant cyanobacteria, relies on as many as 37 different features, most of which are not preserved by silicification.In the hot-spring systems of the TVZ, characterisation of cyanobacteria which have been replaced and encrusted by opal-A is typically restricted to colony morphology, the length, diameter and morphology of the filament, and the presence/absence of septa, branching or a sheath. In many cases, description is limited to a subset of these parameters. Such a limited set of morphological characteristics severely impedes identifications in terms of extant taxa. The physical changes which accompany the stepwise diagenetic progression from opal-A to opal-CT ± opal-C to microcrystalline quartz may lead to further degradation of the silicified microbes and the loss of more taxonomically important features. Clearly, considerable care must be taken when trying to name silicified microorganisms and make palaeoenvironmental inferences.

scholarly journals Weak motion attenuation of peak ground acceleration in the North Island, New Zealand

1999 ◽  
Vol 32 (3) ◽  
pp. 125-145
Author(s):  
Aasha Pancha ◽  
John Taber
Keyword(s):  
New Zealand ◽  
Strong Motion ◽  
Pacific Plate ◽  
Azimuthal Dependence ◽  
Ground Acceleration ◽  
Attenuation Relations ◽  
Absolute Level ◽  
The North ◽  
Anelastic Attenuation ◽  
Attenuation Rate

Attenuation relations using weak ground motion recordings have been determined using data from the New Zealand National Seismograph Network and several temporary seismograph deployments. Models have been developed for earthquake sources in four regions: the Eastern North Island deep and shallow regions and the Central North Island (CNI) deep and shallow regions. Deep events were those with hypocenters below 33 km. Regression coefficients have been determined using the attenuation models of Joyner and Boore (1981) and Molas and Yamazaki (1995). The anelastic attenuation rates in the Eastern North Island expressions are comparable to that of Joyner and Boore (1981), suggesting that weak motion attenuation can be used to estimate variations in strong motion attenuation. However, the absolute level of the strong-motion attenuation curves greatly differs from those of the weak-motion. The anelastic attenuation rate for the shallow CNI is of the order of two to three times that observed for the Eastern North Island. The lowest attenuation rate was found for events within the deep CNI, whose ray paths did not cross the shallow Central North Island region. This is consistent with a low rate of attenuation in the subducting Pacific plate. Azimuthal dependence of PGA is evident within each of the regions. Within the Eastern North Island, the attenuation rate is lowest in the direction of 35-55° from North, which is roughly along the strike of the subducting Pacific plate. A similar azimuthal dependence was also noted within the deep CNI region, while a slightly different minimum direction (5°) was determined for the shallow CNI region.

Hot spring and geyser sinters: the integrated product of precipitation, replacement, and deposition

2003 ◽  
Vol 40 (11) ◽  
pp. 1549-1569 ◽  
Author(s):  
Brian Jones ◽  
R W Renaut
Keyword(s):  
New Zealand ◽  
Hot Spring ◽  
Pollen Grains ◽  
Taupo Volcanic Zone ◽  
Critical Importance ◽  
Volcanic Zone ◽  
The North ◽  
The World ◽  
Siliceous Sinter ◽  
Flow Through

Complex ornate sinter deposits are found in many hot spring and geysers systems throughout the world, including those located in the Taupo Volcanic Zone on the North Island of New Zealand. Those sinters are formed of opal-A that replaced microbes, opal-A precipitated as cement, accessory minerals (e.g., kaolinite, jarosite, calcite), biological detritus (e.g., leaves, wood, pollen grains), and lithic detritus. The opal-A is compositionally variable because of the amount of water (OH and H2O) and, in some cases, accessory elements (e.g., Au, Ag) bound into its structure. The composition and fabric of the siliceous sinter found at any locality reflect the relative balance among the processes of replacement, precipitation, and deposition. The microbes that inhabit these systems are of critical importance because they are commonly replaced by and (or) encrusted with opal-A. In many settings, copious amounts of opal-A are precipitated as cement around the frameworks of silicified filaments. The cementation process, which continues for as long as waters supersaturated with respect to opal-A flow through the sinter, commonly reduces the porosity of the sinters by as much as 50%. This process is probably of far greater significance than has been previously recognized. The textural and compositional complexity of siliceous sinters found in hot spring and geyser systems reflects the myriad of interrelated processes that control their formation.

scholarly journals Tectonic classification of vertical crustal motions – a case study for New Zealand

2016 ◽  
Vol 46 (2) ◽  
pp. 91-109 ◽  
Author(s):  
Robert Tenzer ◽  
Ali Fadil
Keyword(s):  
New Zealand ◽  
Active Tectonics ◽  
Southern Alps ◽  
Taupo Volcanic Zone ◽  
Tectonic Block ◽  
Volcanic Zone ◽  
Tectonic Plates ◽  
The North ◽  
Vertical Displacements

Abstract We investigate the relationship between vertical crustal motion and tectonic block configuration. The study is conducted along the active tectonic margin between the Australian and Pacific tectonic plates in New Zealand with a well-defined tectonic block configuration. For this purpose, the rates of vertical crustal motions relative to the ITRF2008 reference frame are estimated based on processing the GPS data (provided by the GeoNET project) collected at 123 continuous and semi-continuous GPS sites. The numerical results confirmed the uplift of the central Southern Alps at the current rate of 4.5 mm/yr. This tectonic uplift is coupled in the South Island by the subsidence on both sides of the Southern Alps. The detected rates of subsidence in the eastern South Island are typically less than 1 mm/yr. The subsidence in the Buller Region (in the northwest South Island) is 1.4–1.5 mm/yr. Except for the Taupo Volcanic Zone and the upper Raukumara Block (in the central and northeast North Island), the subsidence is prevailing in the North Island. The systematic subsidence up to 9 mm/yr is detected along the Dextral Fault Belt (in the lower North Island). The largest localized vertical displacements (between −10 and 17 mm/yr) in the Taupo Volcanic Zone are attributed to active tectonics, volcanisms and geothermal processes in this region. A classification of these vertical tectonic motions with respect to the tectonic block configuration reveals that most of tectonic blocks are systematically uplifted, subsided or tilted, except for regions characterized by a complex pattern of vertical motions attributed to active geothermal and volcanic processes.

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 Revised isoseismal maps for the 1956 Bay of Plenty and 1987 Edgecumbe, New Zealand, earthquakes

2007 ◽  
Vol 40 (4) ◽  
pp. 200-206
Author(s):  
David J. Dowrick
Keyword(s):  
New Zealand ◽  
Important Implication ◽  
Strong Influence ◽  
Taupo Volcanic Zone ◽  
Volcanic Zone ◽  
High Attenuation ◽  
Damage Costs ◽  
Hazard And Risk ◽  
The Mean ◽  
Isoseismal Maps

The Modified Mercalli intensities of the 1956 Mw 6.3 Bay of Plenty and 1987 Mw 6.5 Edgecumbe earthquakes have recently been reviewed and about one-third of them were found to be erroneous. The resulting revisions to their isoseismal maps are substantial, and both new maps now show the strong influence of the high attenuation in the Taupo Volcanic Zone (TVZ). An analysis of the causes of the errors in the intensities is given. The new maps will help improve the modelling of attenuation in the TVZ, and will contribute to improvements in assessments of seismic hazard and risk in that region. An important implication is that the mean damage ratios estimated from studies of damage costs in the Edgecumbe earthquake by Dowrick and Rhoades are likely to be erroneously low, and need to be reviewed.

scholarly journals Historical incidence of Modified Mercalli intensity in New Zealand and comparisons with hazard models

2003 ◽  
Vol 36 (1) ◽  
pp. 1-24 ◽  
Author(s):  
D. J. Dowrick ◽  
W. J. Cousins
Keyword(s):  
New Zealand ◽  
Seismic Hazard ◽  
First Century ◽  
Taupo Volcanic Zone ◽  
Hazard Models ◽  
Hazard Rates ◽  
Return Periods ◽  
Volcanic Zone ◽  
North West ◽  
The North

The historical incidence of Modified Mercalli intensity produced by earthquakes of magnitude Mw ≥ 5.25 and depth ≤ 100 km has been determined for 47 locations in New Zealand for the period 1840-1997 inclusive. Maps for the return periods of intensities MM4 - MM7 were prepared. The effects of the highly attenuating Taupo Volcanic Zone (TVZ) were shown to be important for hazard both in the zone and in areas to the north-west of it. The rate of occurrence of the higher intensities was found to be about 2.5 times greater in the first century of the study period than in the last 50 years. The historical seismic hazard rates for intensities MM5 and MM6 averaged across the country were found to be approximately half those of the now obsolete Smith & Berryman seismic hazard model, and 70% of those of the more recent Stirling et al model.

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