Recent JGR policies that encourage special sections and eliminate page charges for author‐produced copy have been a boon for JGR‐Solid Earth, at least if the number of pages published is used as the primary measure of success. On the... more
Recent JGR policies that encourage special sections and eliminate page charges for author‐produced copy have been a boon for JGR‐Solid Earth, at least if the number of pages published is used as the primary measure of success. On the other hand, these policies have not served the interests of individual subscribers.The merit of the material published in the 8,557 pages of the 1990 volume of JGR‐Solid Earth is not in question. As a subscriber whose main interest is in seismology, however, I have several measures of the value and cost of the journal besides the number of published pages. These 8,557 pages of JGR‐Solid Earth occupy 29 cm of shelf space and weigh 15.7 kg. (The June issue alone weighed 1.9 kg!) These are awkward figures for anyone contemplating a long‐distance move or just taking the most recent issue home for the evening.
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Over the last decade, a rolling array of seismometers has been sequentially deployed throughout southeast Australia to record passive seismic activity. To date, nearly 350 separate sites have been occupied with nominal station spacings of... more
Over the last decade, a rolling array of seismometers has been sequentially deployed throughout southeast Australia to record passive seismic activity. To date, nearly 350 separate sites have been occupied with nominal station spacings of 40-50 km on the mainland and 15-20 km in Tasmania. Deployment periods for each of the eight arrays installed so far have varied between 4-10
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ABSTRACT We have build a global upper mantle tomographic model of Sv-wave heterogeneities and azimuthal anisotropy as a function of depth, from the analysis of over 100,000 fundamental and higher mode Rayleigh waveforms. The selected... more
ABSTRACT We have build a global upper mantle tomographic model of Sv-wave heterogeneities and azimuthal anisotropy as a function of depth, from the analysis of over 100,000 fundamental and higher mode Rayleigh waveforms. The selected waveforms are mostly associated with epicenter-station paths shorter than 6000 km and typical of regional surface wave tomography at the scale of a tectonic plate. They provide a global coverage of the Earth with an original dataset, less likely to be affected by spurious effects such as multipathing or focusing/defocusing, compared to the longer R1 and R2 paths classically used in global tomography. We observe a peculiar behavior of the fast-moving Australian plate, which appears to be the only continent for which basal drag on the lithosphere is sufficient to cause azimuthal anisotropy aligned with plate motion. Beneath other continents, azimuthal anisotropy vanishes near 150 km depth and supports a frozen-in origin within the lithosphere with no evidence for a deeper layer, which would explain the 1 s delay time typically observed in SKS studies and the good correlation between results from SKS splitting and past tectonics for continents other than Australia. The weak azimuthal anisotropy observed at depth greater than 150 km for continents other than Australia is compatible with simple shear leading to anisotropy with a plunging axis of symmetry.
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Research Interests: Geology and Anisotropy
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Research Interests: Geology, Geochemistry, Geophysics, Seismology, Yilgarn Craton (Precambrian tectonics), and 14 moreTectonophysics, Archean, Seismic Refraction, Fluid flow, Shear Zone, Craton, Three Dimensional, Seismic reflection, Large Scale, South West, Data Type, Surface Wave, Software Package, and receiver function
A series of steps in the lithospheric thickness of eastern Australia are revealed by the latest seismic surface wave tomographic model and calculations of the horizontal gradient of shear wave speed. The new images incorporate data from... more
A series of steps in the lithospheric thickness of eastern Australia are revealed by the latest seismic surface wave tomographic model and calculations of the horizontal gradient of shear wave speed. The new images incorporate data from the recent Tasmal experiment, improving resolution in continental Australia. Through comparisons with surface geology and geochemical studies, it is possible to infer that the steps in lithospheric thickness are related to boundaries between blocks of different age. The westernmost boundary marks the edge of the Archaean to Early‐Proterozoic core of the continent. A second lithospheric boundary is observed in the central part of east Australia. To the west of this line, geochemical evidence suggests that there is Proterozoic lithospheric mantle, and this boundary may therefore represent the change from Proterozoic to Phanerozoic basement. The structure on the eastern margin of the continent is dominated by slow velocities, suggesting that in this are...
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Interpolation of spatial data is a widely used technique across the Earth sciences. For example, the thickness of the crust can be estimated by different active and passive seismic source surveys, and seismologists reconstruct the... more
Interpolation of spatial data is a widely used technique across the Earth sciences. For example, the thickness of the crust can be estimated by different active and passive seismic source surveys, and seismologists reconstruct the topography of the Moho by interpolating these different estimates. Although much research has been done on improving the quantity and quality of observations, the interpolation algorithms utilized often remain standard linear regression schemes, with three main weaknesses: (1) the level of structure in the surface, or smoothness, has to be predefined by the user; (2) different classes of measurements with varying and often poorly constrained uncertainties are used together, and hence it is difficult to give appropriate weight to different data types with standard algorithms; (3) there is typically no simple way to propagate uncertainties in the data to uncertainty in the estimated surface. Hence the situation can be expressed by Mackenzie (2004): “We use f...
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The SEAL3 experiment represents one of the twelve array deployments that so far comprise the large and ambitious WOMBAT project, which aims to cover a significant portion of the Australian continent with a rolling array of seismometers.... more
The SEAL3 experiment represents one of the twelve array deployments that so far comprise the large and ambitious WOMBAT project, which aims to cover a significant portion of the Australian continent with a rolling array of seismometers. SEAL3 consists of 55 three-component short-period instruments located in central and southern New South Wales (NSW) with an average station spacing of approximately
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ABSTRACT Full waveform inversion for upper-mantle structure in the Australasian region based on the spectral-element and adjoint methods
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In the southernmost Ryukyu subduction zone, slab-guiding behavior from intermediate-depth earthquakes is well documented with a low-frequency (<2 Hz) first P arrival followed by sustained high-frequency (3–10 Hz) wave trains. Such... more
In the southernmost Ryukyu subduction zone, slab-guiding behavior from intermediate-depth earthquakes is well documented with a low-frequency (<2 Hz) first P arrival followed by sustained high-frequency (3–10 Hz) wave trains. Such waves developed by propagating along a long path within the slab are expected to have high sensitivity to anisotropy within the slab. We determine shear wave splitting parameters from 178 intraplate events that are deeper than 100 km. The possible slab-anisotropy-associated polarization pattern shows the fast direction at N65°E and delay time of 0.13–0.45 s. This is stronger than the previously documented crust effect (<0.1 s), similar to the mantle wedge effect (0.28 s in average), but weaker than the upper mantle effect (1.3 s in average) in Taiwan. The fast axis reflects the fossil spreading direction of Philippine Sea plate with minor clockwise rotation due to the collision to Eurasian plate.
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The WOMBAT experiment is an ambitious program of rolling passive seismic array deployments designed to cover a significant portion of the Australian continent. Over the last decade, ~450 sites have been occupied in southeast Australia... more
The WOMBAT experiment is an ambitious program of rolling passive seismic array deployments designed to cover a significant portion of the Australian continent. Over the last decade, ~450 sites have been occupied in southeast Australia during the course of 11 separate deployments lasting up to one year. In each case, short period seismometers with a natural frequency of 1 Hz
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Research Interests: Biochemistry, Bioinformatics, Evolutionary Biology, Environmental Science, Developmental Biology, and 15 moreClimate Change, Computational Biology, Biotechnology, Cancer, Biology, Cell Cycle, Ecology, Drug Discovery, Evolution, Astrophysics, Functional Genomics, Astronomy, DNA, Cell Signalling, and Earth Science
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Semblance displays are commonly used to indicate the velocities required to flatten reflection hyperbolas during a velocity analysis of seismic data. "Model-based velocity analysis" is a scheme for interpreting semblance... more
Semblance displays are commonly used to indicate the velocities required to flatten reflection hyperbolas during a velocity analysis of seismic data. "Model-based velocity analysis" is a scheme for interpreting semblance analyses that uses an elastic synthetic seismogram computed from a detailed depth model. The depth model is constructed from logs taken from an adjacent well. The semblance analysis of the synthetic and the P-wave RMS velocity function derived from the depth model are then used to guide the velocity analysis of nearby field records. Semblance analyses of additional synthetics, such as those computed without multiples, enable noise events to be more readily identified. Strong noise events remain identifiable on field data semblance analyses computed away from the well. A model-based approach thereby allows more effective extrapolation of the well-log information. A model-based velocity analysis revealed that interbed multiples had been mistaken for primarie...
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Strong noise contributions currently prevent adequate definition of deep exploration targets in marine seismic data from the Gippsland Basin. We computed an elastic synthetic seismogram (Kennett, 1979, 1980) from a highly detailed depth... more
Strong noise contributions currently prevent adequate definition of deep exploration targets in marine seismic data from the Gippsland Basin. We computed an elastic synthetic seismogram (Kennett, 1979, 1980) from a highly detailed depth model to match the raw field records with considerable accuracy. As part of a sensitivity analysis, we computed additional synthetics to gauge the effects of poorly known parts of the depth model upon the elastic synthetic. These synthetics also helped us to identify noise events in the field records. Subsequent processing of the synthetics led to the identification of persistent noise contributions to stacked data from the Gippsland Basin. Noise contributions in the target zone consist of "shear reflections" resulting from strong mode conversion occurring at the Miocene channels and the Latrobe Group coal/shale sequence. These formations then reconvert the S-waves to P-waves so that they are recorded by the hydrophones. The timing and curv...
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In the period from 1958 to 1996 the Australian National University seismological network has located more than 7600 earthquakes in southeastern Australia with a network concentrated between Canberra and Sydney. This catalogue of... more
In the period from 1958 to 1996 the Australian National University seismological network has located more than 7600 earthquakes in southeastern Australia with a network concentrated between Canberra and Sydney. This catalogue of earthquakes provides a good database for the analysis of the temporal and spatial distribution of events in the region. For the area 37–33°S, 147–151°E, the catalogue is
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Genetic algorithm (GA) inversion, a nonlinear global optimization technique, has been applied to determine crustal and uppermost mantle velocity structure from teleseismic receiver functions. With a new modelling in which not only the S... more
Genetic algorithm (GA) inversion, a nonlinear global optimization technique, has been applied to determine crustal and uppermost mantle velocity structure from teleseismic receiver functions. With a new modelling in which not only the S wave velocity but also the layer thickness and the VP/VS ratio are model parameters, the GA receiver function inversion is able to recover the velocity structure
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ABSTRACT Seismic data coverage of Australia has greatly increased over the last 10 years, providing an opportunity to update the seismological model of the continent. Good seismological models of the Earth&#39;s crust and upper mantle... more
ABSTRACT Seismic data coverage of Australia has greatly increased over the last 10 years, providing an opportunity to update the seismological model of the continent. Good seismological models of the Earth&#39;s crust and upper mantle are critical for many tasks, such as the calculation of earthquake source parameters, regional hazard modelling and imaging of lithospheric dynamic processes. The AuSREM project aims to produce a fully interpolable seismological model of the Australian continent with a 0.5-degree resolution down to 500 km depth. It will include a detailed crustal model of P-wave speed, S-wave speed, density and depth to major boundaries. The mantle component of the model is likely to be less detailed but will also include P-wave speed, S-wave speed and density. Ultimately this model will be publicly available and will provide a base model for other research. The AuSREM model will be a collaborative effort relying on the integration of a wide variety of data sources. For the crustal component data sources include refraction surveys, receiver function studies, reflection surveys, crustal tomography, gravity interpretation and sediment thickness databases. This should improve upon the Crust 2.0 model for the region, as there has been a large amount of data collected since this model was compiled. The mantle component will rely mainly on tomography. Where there is insufficient data to provide 0.5-degree resolution data interpolation methods will be used to fill the gaps. AuSREM is an extension of the AusMoho project, which maps the depth to Moho in Australia. The new Moho map includes over 12000 km of deep seismic reflection profiles and 600 data points from seismic refraction experiments, permanent seismic stations, 3-component broadband and short-period stations. The Moho map produced provides us with our first fundamental boundary for the AuSREM model.