Finite-frequency imaging of the global 410- and 660-km discontinuities using SS precursors

SUMMARY We report finite-frequency imaging of the global 410- and 660-km discontinuities using boundary sensitivity kernels for traveltime measurements made on SS precursors. The application of finite-frequency sensitivity kernels overcomes resolution limits in previous studies associated with large Fresnel zones of SS precursors and their interferences with other seismic phases. In this study, we calculate the finite-frequency sensitivities of SS waves and their precursors based on a single-scattering (Born) approximation in the framework of travelling-wave mode summation. The global discontinuity surface is parametrized using a set of triangular gridpoints with a lateral spacing of about 4°, and we solve the linear finite-frequency inverse problem (2-D tomography) based on singular value decomposition (SVD). The new global models start to show a number of features that were absent (or weak) in ray-theoretical back-projection models at spherical harmonic degree l > 6. The thickness of the mantle transition zone correlates well with wave speed perturbations at a global scale, suggesting dominantly thermal origins for the lateral variations in the mantle transition zone. However, an anticorrelation between the topography of the 410-km discontinuity and wave speed variations is not observed at a global scale. Overall, the mantle transition zone is about 2–3 km thicker beneath the continents than in oceanic regions. The new models of the 410- and 660-km discontinuities show better agreement with the finite-frequency study by Lawrence & Shearer than other global models obtained using SS precursors. However, significant discrepancies between the two models exist in the Pacific Ocean and major subduction zones at spherical harmonic degree >6. This indicates the importance of accounting for wave interactions in the calculations of sensitivity kernels as well as the use of finite-frequency sensitivities in data quality control.

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Triplicated P-wave measurements for waveform tomography of the mantle transition zone

Solid Earth ◽

10.5194/se-3-339-2012 ◽

2012 ◽

Vol 3 (2) ◽

pp. 339-354 ◽

Cited By ~ 21

Author(s):

S. C. Stähler ◽

K. Sigloch ◽

T. Nissen-Meyer

Keyword(s):

Transition Zone ◽

Epicentral Distance ◽

Body Wave ◽

Source Parameters ◽

Body Waves ◽

P Wave ◽

Theoretical Modelling ◽

Finite Frequency ◽

Mantle Transition Zone ◽

Band Limited

Abstract. Triplicated body waves sample the mantle transition zone more extensively than any other wave type, and interact strongly with the discontinuities at 410 km and 660 km. Since the seismograms bear a strong imprint of these geodynamically interesting features, it is highly desirable to invert them for structure of the transition zone. This has rarely been attempted, due to a mismatch between the complex and band-limited data and the (ray-theoretical) modelling methods. Here we present a data processing and modelling strategy to harness such broadband seismograms for finite-frequency tomography. We include triplicated P-waves (epicentral distance range between 14 and 30°) across their entire broadband frequency range, for both deep and shallow sources. We show that is it possible to predict the complex sequence of arrivals in these seismograms, but only after a careful effort to estimate source time functions and other source parameters from data, variables that strongly influence the waveforms. Modelled and observed waveforms then yield decent cross-correlation fits, from which we measure finite-frequency traveltime anomalies. We discuss two such data sets, for North America and Europe, and conclude that their signal quality and azimuthal coverage should be adequate for tomographic inversion. In order to compute sensitivity kernels at the pertinent high body wave frequencies, we use fully numerical forward modelling of the seismic wavefield through a spherically symmetric Earth.

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Phase change in subducted lithosphere, impulse, and quantizing Earth surface deformations

Solid Earth ◽

10.5194/se-6-1075-2015 ◽

2015 ◽

Vol 6 (3) ◽

pp. 1075-1085

Author(s):

C. O. Bowin ◽

W. Yi ◽

R. D. Rosson ◽

S. T. Bolmer

Keyword(s):

Angular Momentum ◽

Phase Change ◽

Spherical Harmonic ◽

Plate Tectonics ◽

Phase Changes ◽

Metallic Nickel ◽

Spherical Harmonic Degree ◽

The Pacific ◽

Seamount Chain ◽

Harmonic Degree

Abstract. The new paradigm of plate tectonics began in 1960 with Harry H. Hess's 1960 realization that new ocean floor was being created today and is not everywhere of Precambrian age as previously thought. In the following decades an unprecedented coming together of bathymetric, topographic, magnetic, gravity, seismicity, seismic profiling data occurred, all supporting and building upon the concept of plate tectonics. Most investigators accepted the premise that there was no net torque amongst the plates. Bowin (2010) demonstrated that plates accelerated and decelerated at rates 10−8 times smaller than plate velocities, and that globally angular momentum is conserved by plate tectonic motions, but few appeared to note its existence. Here we first summarize how we separate where different mass sources may lie within the Earth and how we can estimate their mass. The Earth's greatest mass anomalies arise from topography of the boundary between the metallic nickel–iron core and the silicate mantle that dominate the Earth's spherical harmonic degree 2 and 3 potential field coefficients, and overwhelm all other internal mass anomalies. The mass anomalies due to phase changes in olivine and pyroxene in subducted lithosphere are hidden within the spherical harmonic degree 4–10 packet, and are an order of magnitude smaller than those from the core–mantle boundary. Then we explore the geometry of the Emperor and Hawaiian seamount chains and the 60° bend between them that aids in documenting the slow acceleration during both the Pacific Plate's northward motion that formed the Emperor seamount chain and its westward motion that formed the Hawaiian seamount chain, but it decelerated at the time of the bend (46 Myr). Although the 60° change in direction of the Pacific Plate at of the bend, there appears to have been nary a pause in a passive spreading history for the North Atlantic Plate, for example. This, too, supports phase change being the single driver for plate tectonics and conservation of angular momentum. Since mountain building we now know results from changes in momentum, we have calculated an experimental deformation index value (1–1000) based on a world topographic grid at 5 arcmin spacing and displayed those results for viewing.

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Mantle transition zone structure beneath India and Western China from migration of PP and SS precursors

Geophysical Journal International ◽

10.1093/gji/ggt511 ◽

2014 ◽

Vol 197 (1) ◽

pp. 396-413 ◽

Cited By ~ 16

Author(s):

S. Lessing ◽

C. Thomas ◽

S. Rost ◽

L. Cobden ◽

D. P. Dobson

Keyword(s):

Transition Zone ◽

Western China ◽

Zone Structure ◽

Mantle Transition Zone ◽

Ss Precursors

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Imaging the upper mantle transition zone with a generalized Radon transform of SS precursors

Physics of The Earth and Planetary Interiors ◽

10.1016/j.pepi.2010.02.006 ◽

2010 ◽

Vol 180 (1-2) ◽

pp. 80-91 ◽

Cited By ~ 20

Author(s):

Q. Cao ◽

P. Wang ◽

R.D. van der Hilst ◽

M.V. de Hoop ◽

S.-H. Shim

Keyword(s):

Transition Zone ◽

Radon Transform ◽

Upper Mantle ◽

Mantle Transition Zone ◽

Generalized Radon Transform ◽

Ss Precursors

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Resonant Coupling between Solar Gravity Modes

International Astronomical Union Colloquium ◽

10.1017/s0252921100095622 ◽

1983 ◽

Vol 66 ◽

pp. 259-266

Author(s):

W. Dziembowski

Keyword(s):

Parametric Resonance ◽

Spherical Harmonic ◽

Finite Amplitude ◽

Linear Instability ◽

Spherical Harmonic Degree ◽

Strongly Coupled ◽

Resonant Coupling ◽

High Degree ◽

Harmonic Degree ◽

Solar Gravity

AbstractIt is shown that in consequence of the parametric resonance, g modes of low spherical harmonic degree l are strongly coupled to the modes of high degree. The coupling limits the growth of lowl modes to very small amplitudes. For g1, l = 1 mode, the final amplitude of the radial velocity is of the order of 10 cm s-1. A mixing of solar core as a result of a finite-amplitude development of linear instability of this mode is thus highly unlikely.

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Truncated co-seismic geoid and gravity changes in the domain of spherical harmonic degree

Earth Planets and Space ◽

10.1186/bf03352535 ◽

2004 ◽

Vol 56 (9) ◽

pp. 881-892 ◽

Cited By ~ 7

Author(s):

Wenke Sun ◽

Shuhei Okubo

Keyword(s):

Spherical Harmonic ◽

Spherical Harmonic Degree ◽

Gravity Changes ◽

Harmonic Degree

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Multiwavelength studies of β Cephei stars

Symposium - International Astronomical Union ◽

10.1017/s0074180900214368 ◽

1994 ◽

Vol 162 ◽

pp. 17-18

Author(s):

H. Cugier ◽

A. Pigulski ◽

G. Polubek ◽

R. Monier

Keyword(s):

Chemical Composition ◽

Radial Velocity ◽

Spherical Harmonic ◽

Present Knowledge ◽

Velocity Data ◽

Spherical Harmonic Degree ◽

Pulsating Stars ◽

Radial Velocity Data ◽

Harmonic Degree

As first pointed out by Moskalik and Dziembowski (1992) all β Cephei stars lie within the domain of H–R diagram where κ-mechanism effectively drives pulsations in the stellar layers with T ≈ 2×105 K. For most of these objects a chemical composition described by X = 0.70 and Z = 0.02 is sufficient to account for the pulsations, cf. Dziembowski and Pamyatnykh (1993). Recently, Cugier, Dziembowski and Pamyatnykh (1993) have investigated how the present knowledge about nonadiabatic observables of β Cephei stars affects methods of identification of the spherical harmonic degree, l. They found that good photometric and radial velocity data should result in unambiguous identification of l. Cugier, Dziembowski and Pamyatnykh also concluded that nonadiabatic observables can be used to obtain mean stellar parameters of pulsating stars.

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Subduction to the lower mantle – a comparison between geodynamic and tomographic models

Solid Earth ◽

10.5194/se-3-415-2012 ◽

2012 ◽

Vol 3 (2) ◽

pp. 415-432 ◽

Cited By ~ 19

Author(s):

B. Steinberger ◽

T. H. Torsvik ◽

T. W. Becker

Keyword(s):

Cross Sections ◽

Upper Mantle ◽

Spherical Harmonic ◽

Lower Mantle ◽

Subduction Zones ◽

Shear Velocity ◽

Mantle Flow ◽

Spherical Harmonic Degree ◽

Geodynamic Model ◽

Harmonic Degree

Abstract. It is generally believed that subduction of lithospheric slabs is a major contribution to thermal heterogeneity in Earth's entire mantle and provides a main driving force for mantle flow. Mantle structure can, on the one hand, be inferred from plate tectonic models of subduction history and geodynamic models of mantle flow. On the other hand, seismic tomography models provide important information on mantle heterogeneity. Yet, the two kinds of models are only similar on the largest (1000 s of km) scales and are quite different in their detailed structure. Here, we provide a quantitative assessment how good a fit can be currently achieved with a simple viscous flow geodynamic model. The discrepancy between geodynamic and tomography models can indicate where further model refinement could possibly yield an improved fit. Our geodynamical model is based on 300 Myr of subduction history inferred from a global plate reconstruction. Density anomalies are inserted into the upper mantle beneath subduction zones, and flow and advection of these anomalies is calculated with a spherical harmonic code for a radial viscosity structure constrained by mineral physics and surface observations. Model viscosities in the upper mantle beneath the lithosphere are ~1020 Pas, and viscosity increases to ~1023 Pas in the lower mantle above D". Comparison with tomography models is assessed in terms of correlation, both overall and as a function of depth and spherical harmonic degree. We find that, compared to previous geodynamic and tomography models, correlation is improved, presumably because of advances in both plate reconstructions and mantle flow computations. However, high correlation is still limited to lowest spherical harmonic degrees. An important ingredient to achieve high correlation – in particular at spherical harmonic degree two – is a basal chemical layer. Subduction shapes this layer into two rather stable hot but chemically dense "piles", corresponding to the Pacific and African Large Low Shear Velocity Provinces. Visual comparison along cross sections indicates that sinking speeds in the geodynamic model are somewhat too fast, and should be 2 ± 0.8 cm yr−1 to achieve a better fit.

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