Global seismic tomography of the mantle

Dziewoński, Adam M.

doi:10.1029/95rg00738

Cited by 30 publications

(7 citation statements)

References 70 publications

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“…Tomographic models, derived from global or regional studies, agree reasonably well, at least between 100 and 600 km, on the long wavelength structure, i.e. the first 12 degrees in spherical harmonics with a spatial resolution of the order of 1500 km at the surface (Dziewonski 1995; Ritzwoller & Lavely 1995). Regional tomographic models tend, however, to predict somewhat higher power spectral density at shorter wavelengths than can be resolved in global studies (Chevrot et al 1998).…”

Section: Introductionmentioning

confidence: 73%

Coupling the spectral element method with a modal solution for elastic wave propagation in global earth models

Capdeville

Chaljub

Montagner

2003

Geophysical Journal International

128

104

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International audienceWe present a new method for wave propagation in global earth models based upon the coupling between the spectral element method and a modal solution method. The Earth is decomposed into two parts, an outer shell with 3-D lateral heterogeneities and an inner sphere with only spherically symmetric heterogeneities. Depending on the problem, the outer heterogeneous shell can be mapped as the whole mantle or restricted only to the upper mantle or the crust. In the outer shell, the solution is sought in terms of the spectral element method, which stem from a high order variational formulation in space and a second-order explicit scheme in time. In the inner sphere, the solution is sought in terms of a modal solution in frequency after expansion on the spherical harmonics basis. The spectral element method combines the geometrical flexibility of finite element methods with the exponential convergence rate of spectral methods. It avoids the pole problems and allows for local mesh refinement, using a non-conforming discretization, for the resolution of sharp variations and topography along interfaces. The modal solution allows for an accurate isotropic representation in the inner sphere. The coupling is introduced within the spectral element method via a Dirichlet-to-Neumann (DtN) operator. The operator is explicitly constructed in frequency and in generalized spherical harmonics. The inverse transform in space and time requires special attention and an asymptotic regularization. The coupled method allows a significant speed-up in the simulation of the wave propagation in earth models. For spherically symmetric earth model, the method is shown to have the accuracy of spectral transform methods and allow the resolution of wavefield propagation, in 3-D laterally heterogeneous models, without any perturbation hypothesis

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Section: Introductionmentioning

confidence: 73%

Coupling the spectral element method with a modal solution for elastic wave propagation in global earth models

Capdeville

Chaljub

Montagner

2003

Geophysical Journal International

128

104

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“…More specifically, global tomography gives an indication of a reddening of the spatial spectrum of heterogeneity in both the lower and upper mantle, with a white spectrum of heterogeneity in the midmantle up to harmonic order 10-12. These harmonic orders correspond to scale lengths on the order of 2000 km [Dziewonski, 1995]. The hypothesis that the D" discontinuity may result from a change in the statistics of small-scale heterogeneity has important consequences for our understanding of mantle dynamics, not necessarily requiring the existence of a thick, relatively homogeneous, chemically distinct or solid phase changed layer at the lower mantle.…”

Section: Resultsmentioning

confidence: 99%

“…Thus far, three types of change of heterogeneity statistics in D" have been tested for effects on broadband S 4-ScS (Figure 3 [ Tackley, 1998] and tomographic modeling [Dziewonski, 1995], which suggest a reddening of the heterospectrum in D" at small wavenumbers in the lower mantle. More specifically, global tomography gives an indication of a reddening of the spatial spectrum of heterogeneity in both the lower and upper mantle, with a white spectrum of heterogeneity in the midmantle up to harmonic order 10-12.…”

Section: Resultsmentioning

confidence: 99%

D″ as a transition in the heterogeneity spectrum of the lowermost mantle

Cormier¹

2000

J. Geophys. Res.

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Abstract. Broadband $H and P wave fields are pseudospectrally modeled in three forms of the heterogeneity spectrum of the mantle, each having a transition in the power spectrum of heterogeneity in the lowermost mantle. With D" defined as a zone of increased heterogeneity, low-pass and high-pass filters of models of the heterogeneity spectrum demonstrate that the thickness of D" inferred from an incident seismic wave field can depend on the dominant wavelength of that wave field. A model of D" heterogeneity that agrees with the coda power between S and ScS and between P and PcP is a simple linear extrapolation of the spectrum of heterogeneity power versus depth determined from global tomography to wavenumbers corresponding to short-period body waves. The negligible decay in the power spectrum of heterogeneity across a band of wavenumbers from 0.0001 to 1 km -• is consistent with a pervasive entrainment of small scale chemical heterogeneities by convective motions. The lack of strong scattering attenuation in observed $cS and PcP waveforms is used to establish upper bounds in this wavenumber band of 3% and 1.5% on the root-mean-square variations of S and P velocity, respectively. Some realizations of the preferred model of the heterogeneity spectrum generate an $dS waveform from scattering by an elongated, high velocity anomaly, roughly parallel to the core-mantle boundary. The high topography of similarly shaped anomalies needed to account for the amplitude of narrow angle scattering observed from D" argues against such anomalies having the high-density perturbation expected for a chemically distinct or phase-transformed layer.

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“…Tomographic imaging of mantle structure has been a favored tool of seismologists for more than twenty years, and has resulted in numerous 3-D models of the Earth's interior. Summaries can be found in Romanowicz [1991], Iyer andHirahara [1993], Nolet et al [1994], Ritzwoller and Lavely [1995], Dziewonski [1995], and Masters and Shearer [1995]. In recent years both the abundance and quality of body wave and surface wave data have increased dramatically.…”

Section: Introductionmentioning

confidence: 99%

Seismic tomography with irregular meshes

Sambridge

Rawlinson

2005

Seismic Earth: Array Analysis of Broadband Seismograms

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The current state of seismic tomography using irregular parameterizations is described. A review is given of previous work in the area covering local, regional and global seismic applications. The potential advantage of an irregular parameterization over a regular (uniform) one is that, by introducing higher resolution grids in particular parts of the model, one can maximize the information extracted from the data. Although irregular parameterizations have only recently been used in 3-D mantle tomography, their origins can be traced back more than twenty years. The use of irregular meshes in two and three dimensional tomographic imaging creates a number of 'implementation' issues, not seen with uniform grids. An outline of algorithms for solving all of these bookkeeping problems arising in cubic, tetrahedral or polygonal meshes is included, and references given to more detailed descriptions. Some recent implementations of tomography are discussed where the parameterization is refined during the course of the inversion process. Two examples of adaptive tomography in non-seismic problems suggest that the gradual refinement of the parameterization may be an effective way to regularize the inverse problem. The intention here is to point out the potential advantages and pitfalls of using an irregular parameterization in tomography. At present experience with seismic problems is rather limited (especially in 3-D) and an optimal approach is yet to emerge.

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Global seismic tomography of the mantle

Cited by 30 publications

References 70 publications

Coupling the spectral element method with a modal solution for elastic wave propagation in global earth models

Coupling the spectral element method with a modal solution for elastic wave propagation in global earth models

D″ as a transition in the heterogeneity spectrum of the lowermost mantle

Seismic tomography with irregular meshes

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