Eos, Transactions American Geophysical Union, 1992
Recent JGR policies that encourage special sections and eliminate page charges for author‐produce... 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.
Over the last decade, a rolling array of seismometers has been sequentially deployed throughout s... 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
ABSTRACT We have build a global upper mantle tomographic model of Sv-wave heterogeneities and azi... 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.
A series of steps in the lithospheric thickness of eastern Australia are revealed by the latest s... 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...
Journal of Geophysical Research: Solid Earth, 2012
Interpolation of spatial data is a widely used technique across the Earth sciences. For example, ... 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...
The SEAL3 experiment represents one of the twelve array deployments that so far comprise the larg... 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
ABSTRACT Full waveform inversion for upper-mantle structure in the Australasian region based on t... more ABSTRACT Full waveform inversion for upper-mantle structure in the Australasian region based on the spectral-element and adjoint methods
In the southernmost Ryukyu subduction zone, slab-guiding behavior from intermediate-depth earthqu... 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.
Eos, Transactions American Geophysical Union, 1992
Recent JGR policies that encourage special sections and eliminate page charges for author‐produce... 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.
Over the last decade, a rolling array of seismometers has been sequentially deployed throughout s... 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
ABSTRACT We have build a global upper mantle tomographic model of Sv-wave heterogeneities and azi... 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.
A series of steps in the lithospheric thickness of eastern Australia are revealed by the latest s... 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...
Journal of Geophysical Research: Solid Earth, 2012
Interpolation of spatial data is a widely used technique across the Earth sciences. For example, ... 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...
The SEAL3 experiment represents one of the twelve array deployments that so far comprise the larg... 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
ABSTRACT Full waveform inversion for upper-mantle structure in the Australasian region based on t... more ABSTRACT Full waveform inversion for upper-mantle structure in the Australasian region based on the spectral-element and adjoint methods
In the southernmost Ryukyu subduction zone, slab-guiding behavior from intermediate-depth earthqu... 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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