Imaging New Zealand S Crustal Structure Using Ambient Seismic Noise Recordings From Permanent And Temporary Instruments
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Imaging New Zealand S Crustal Structure Using Ambient Seismic Noise Recordings From Permanent And Temporary Instruments
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Author : Yannik D. Behr
language : en
Publisher:
Release Date : 2011
Imaging New Zealand S Crustal Structure Using Ambient Seismic Noise Recordings From Permanent And Temporary Instruments written by Yannik D. Behr and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2011 with Geology, Structural categories.
3 D Tomographic Imaging Of The Southeast Australian Crust
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Author : Simone Pilia
language : en
Publisher:
Release Date : 2014
3 D Tomographic Imaging Of The Southeast Australian Crust written by Simone Pilia and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2014 with categories.
Seismic tomography is arguably the most powerful geophysical method for imaging the Earth's interior. From its origins in the early 1970s, rapid growth in computing power, increased availability of high quality digital data, and ongoing technique development have all conspired to propel it to a stage where images of unprecedented detail are now produced on a regular basis. In this thesis, cutting edge seismic tomography methods will be used to image 3-D crustal structure in southeast Australia, with the aim of better understanding the tectonic evolution of the former east Gondwana margin. A key objective of the first strand of this thesis is to use data from an array of 24 seismometers to image the crust beneath the Flinders Ranges by using Local Earthquake Tomography. A subset of P- and S-wave traveltimes is inverted to jointly recover earthquake hypocenters, P-wave velocity structure and Vp/Vs anomalies to improve our understanding of crustal structure, rheology, and the mechanism responsible for the localised intraplate deformation that characterises this area. Clusters of seismicity are observed within distinct low velocity regions (i.e., between the Archean-Mesoproterozoic Gawler Craton and the Palaeo-Mesoproterozoic Curnamona Province and along a major sequence of N-S trending Ross-Delamerian thrust faults). I postulate that pre-existing mechanical weaknesses in the lithosphere, principally due to structure and composition, exert first-order control on the distribution of seismicity in the Flinders Ranges. In the second strand of my research, ambient noise data from an array of 24 seismometers is used to produce a 3-D crustal shear wave velocity model of Bass Strait, the key to understanding the missing link between Tasmania and mainland Australia. I apply a transdimensional, hierarchical Bayesian inversion approach to construct a 3-D shear wave velocity model of the area. This allows the entire crust beneath Bass Strait to be imaged in high detail and elucidates the geometry and position of key crustal features. A key feature of the 3-D tomography model is a distinct mid-lower crustal NW-SE high velocity zone that extends from northwestern Tasmania to south-central Victoria, confirming a Proterozoic geological connection that has not previously been established in the deep crust. A recent study that uses 3-D geodynamic modelling has controversially suggested that the entrainment of exotic continental fragments may exert first-order control on continental growth via subduction accretion. Evidence from kinematic modelling suggests that the pre-Carboniferous Tasmanides in southeastern Australia may have been subjected to this process. In the final strand of my research, I present the first high-resolution crustal 3-D shear velocity model of southeastern Australia by applying the same inversion approach that was used for the Bass Strait datasets to seismic noise recorded by the WOMBAT seismic array. The main elements of the proposed continental accretionary model are fully imaged here for the first time, including the remains of the ingested continental fragment and the tectonic escape of the back arc region. To date, no other geophysical study has revealed structures in the deep crust related to the entrainment of continental fragments at former convergent accretionary margins.
Crustal Structure Project
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Author : New Zealand. Department of Scientific and Industrial Research
language : en
Publisher:
Release Date : 1957
Crustal Structure Project written by New Zealand. Department of Scientific and Industrial Research and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 1957 with Earth categories.
Crustal Structure Studies In New Zealand
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Author : Timothy A. Stern
language : en
Publisher:
Release Date : 1986
Crustal Structure Studies In New Zealand written by Timothy A. Stern and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 1986 with Earth (Planet) categories.
Multi Component Ambient Seismic Noise Tomography Of The Auckland Volcanic Field
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Author : Josiah Ensing
language : en
Publisher:
Release Date : 2020
Multi Component Ambient Seismic Noise Tomography Of The Auckland Volcanic Field written by Josiah Ensing and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2020 with Geodynamics categories.
Auckland, New Zealand's most populous region (1.6 million), is situated over an active volcanic field of at least 53 volcanoes. The mechanism driving volcanism in the Auckland Volcanic Field is not well understood. We aim to increase knowledge of the structure of the crust across the Auckland Volcanic Field through multicomponent ambient noise tomography. We hope this will contribute toward understanding possible structural controls on volcanism. We first estimated the orientation of borehole seismometers by polarization analysis of estimates of the Rayleigh wave Green's function, retrieved from ambient noise cross-correlation. Knowing the orientations, we then computed multi-component estimates of Rayleigh wave Green's functions. We performed frequency-time analysis on the Green's functions to extract Rayleigh wave dispersion information. We then used Rayleigh wave group arrival times to perform a reversible-jump Markov chain Monte Carlo inversion for Rayleigh wave speed maps. We took dispersion curves from the Rayleigh wave speed maps, and performed a damped inversion of each dispersion curve for a 60-layer 1D shear speed model. Lastly, we then stitched the 1D models together, creating a pseudo-3D shear speed model. The 3D model is a considerable improvement compared to previous tomographic models, being more robust and having improved resolution. The model best resolved the upper-most crust but has also been able to resolve some features as deep as 25 km. One of the main features in the model is a NNW-SSE boundary slightly east of the Junction Magnetic Anomaly and the volcanic centres of the AVF. This boundary more clearly defines an eastern high speed region and a western low speed region in the upper 5 km divided. We interpret the high speed region as the Waipapa Terrane, and the low speed region as the Murihiku Terrane. Deeper we see a reversal, with a high speed region west of the boundary and a low speed region in the east. We interpret the high speed region to be the continuation of the Dun Mountain-Maitai Terrane, and the low speed region in the east an effect of metamorphic weakening of lower parts of the Waipapa Terrane. We identify a long low speed zone along the NNW-SSE boundary, and other features indicating possible connections to faults and the Takapuna gravity anomaly.
Ambient Seismic Noise Tomography In The Auckland Volcanic Field
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Author : Josiah Ensing
language : en
Publisher:
Release Date : 2015
Ambient Seismic Noise Tomography In The Auckland Volcanic Field written by Josiah Ensing and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2015 with Earthquake hazard analysis categories.
Auckland, New Zealand's most populous region (1.4 million), is situated over a monogenetic volcanic field of at least 53 volcanoes. The most recent eruption in the Auckland Volcanic Field (AVF) was 600 years ago, therefore the AVF is considered active. The risk and hazard of a volcanic eruption in Auckland are difficult to assess. It has been difficult to produce a high resolution model of the subsurface structure of Auckland due to its low seismicity. However, because of New Zealand's long coastlines, Auckland experiences high energy ocean wave generated seismic noise. This study is the first to use ocean noise to infer the structure of the Auckland subsurface. We successfully incorporated a University of Auckland borehole seismometer from Rangitoto Island (RBAZ) into an existing network of GeoNet seismometers in Auckland. We were able to correct for the different instrument responses of the 12 seismometers. The vertical components of 200 days of noisy wavefields from 66 possible station pairs were cross-correlated to estimate the impulse response; this way, the resulting time series is as if one of the stations is a seismic source, and the other a receiver. Using these 66 impulse responses, we estimated Rayleigh wave group and phase velocity dispersion relations by multiple filter analysis. Frequency-dependent surface wave speeds with periods between 3 and 10 seconds provided robust information about the subsurface. We inverted group and phase velocity dispersion curves for shear velocities near the surface to approximately 25 km depth. We found that shear velocity variations correlate well with the crust type and surface geology. The distribution of low-velocity zones shows good spatial correlation with the Murihiku and Waipapa Terranes (semi-continental crust). Models with monotonically increasing shear wave velocity mainly associated with the Dun Mountain Ophiolite Belt, of the Maitai Terrane (oceanic crust). Near the surface (0-1.5 km), basement rock exposures correlated well with higher shear wave velocities, while soft cover rock and poorly consolidated sediments correlated with lower velocities. The average of our 16 models also largely agrees with a shear velocity model obtained by joint teleseismic receiver functions and seismic surface wave inversion techniques by Horspool et al. (2006).
New Zealand Seismological Report
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Author : Seismological Observatory (New Zealand)
language : en
Publisher:
Release Date : 2000
New Zealand Seismological Report written by Seismological Observatory (New Zealand) and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2000 with Seismology categories.
Seismic Imaging Of Crustal Structure At Mid Ocean Ridges
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Author : Anthony James Day
language : en
Publisher:
Release Date : 2001
Seismic Imaging Of Crustal Structure At Mid Ocean Ridges written by Anthony James Day and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2001 with categories.
Bulletin Of The New Zealand National Society For Earthquake Engineering
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Author : New Zealand National Society for Earthquake Engineering
language : en
Publisher:
Release Date : 1985
Bulletin Of The New Zealand National Society For Earthquake Engineering written by New Zealand National Society for Earthquake Engineering and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 1985 with Buildings categories.
Velocity Structure Of The Whataroa Valley Using Ambient Noise Tomography
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Author : Andrew T. McNab
language : en
Publisher:
Release Date : 2017
Velocity Structure Of The Whataroa Valley Using Ambient Noise Tomography written by Andrew T. McNab and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2017 with Geophysics categories.
This thesis applies ambient noise tomography to investigate the shallow structure of the Whataroa Valley. Ambient noise techniques are applied to continuous seismic recordings acquired on 158 geophones deployed during the Whataroa Active Source Seismic Experiment. Despite only having four days of data, a robust shear-wave velocity model is calculated using a phase-weighted stacking approach to improve the cross-correlation functions' signal-to-noise ratios, allowing for robust velocity measurements to be obtained between periods of 0.3 and 1.8\,s. This yields a database of 12,500 vertical component cross correlation functions and the corresponding Rayleigh wave phase and group velocity dispersion curves. Linearised straight-ray tomography is applied to phase and group velocity dispersion measurements at periods ranging from periods of 0.3 to 1.8\,s. The tomography reveals a velocity that decreases from the vicinity of the DFDP-2B borehole to the centre of the valley. This is interpreted to be the geologic basement deepening towards the centre of the valley. A Monte-Carlo inversion technique is used to jointly invert Rayleigh-wave phase and group velocity dispersion curves constructed from phase and group velocity tomography maps of successively higher periods. Linear interpolation of the resulting 1D shear-wave velocity profiles produces a pseudo-3D velocity model of the uppermost 1,000\,m of the Whataroa Valley. Using sharp increases in velocity to represent lithological change, we interpret two velocity contours at 1,150 and 1,250\,m/s as potential sediment-basement contacts. Depth isocontours of these velocities reveal that the basement deepens towards the centre of the valley, reaching a maximum depth of 400 or 600\,m for the 1,150 and 1,250\,m/s velocity contours respectively. These depths indicate strong glacial over-deepening and have implications for future drilling projects in the Whataroa Valley. A sharp velocity increase of 200\,m/s also occurs at 100\,m