A global shear velocity model of the upper mantle from fundamental and higher Rayleigh mode measurements

Debayle, E.; Ricard, Yanick

doi:10.1029/2012jb009288

Cited by 100 publications

(131 citation statements)

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“…The exceptions are the South Indian shield and the North China craton, neither of which has a deep, high wave-speed β h (z) root. The cratonic roots extend somewhat deeper in the CAM2016SH models than they do in the comparable β v (z) models (Debayle & Ricard 2012;Priestley & McKenzie 2013). Gung et al (2003) suggest that roots of continental shields appear deeper in β h (z) models than they do in β v (z) models due to radial anisotropy arising from present-day asthenospheric flow aligning the mineral fabric leading to the strong fast β h (z) signature.…”

Section: The Regionalizationmentioning

confidence: 80%

“…The criteria for successfully fitting the waveform are the same as given in Debayle & Ricard (2012). The waveform fit is successful if the secondary observables are fit, the inversion converges to a unique model, and the observed Love waveform is well matched by the final inversion synthetic waveform.…”

Section: Extracting and Fitting The Secondary Observablesmentioning

confidence: 99%

“…Including overtones in the tomography not only constrains deeper structure better than does the fundamental mode, the overtones improve resolution at shallower depths. An advantage in using the Debayle & Ricard (2012) implementation of the Cara & Lévêque (1987) method over other automated waveform inversion procedures is that it does not require separating the fundamental mode and overtones into unique time windows before making the wave speed measurements since the observed seismogram is modelled as a sum of interfering modes.…”

Section: Extracting Structure Of the Upper Mantlementioning

confidence: 99%

“…Extracting the secondary observables (Cara & Lévêque 1987) and inverting them for the path average velocity structure follows closely the method employed by Debayle & Ricard (2012) but adapted to transverse component seismograms. The secondary observables are measured using cross-correlation.…”

Section: Extracting and Fitting The Secondary Observablesmentioning

confidence: 99%

“…In this study, we have adapted the Rayleigh wave inversion routines of Debayle & Ricard (2012) so as to invert Love waveforms. We show that this procedure can recover velocity structure of the upper mantle to transition zone depths.…”

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confidence: 99%

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A global horizontal shear velocity model of the upper mantle from multimode Love wave measurements

Ho¹,

Priestley²,

Debayle

2016

Geophys. J. Int.

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S U M M A R YSurface wave studies in the 1960s provided the first indication that the upper mantle was radially anisotropic. Resolving the anisotropic structure is important because it may yield information on deformation and flow patterns in the upper mantle. The existing radially anisotropic models are in poor agreement. Rayleigh waves have been studied extensively and recent models show general agreement. Less work has focused on Love waves and the models that do exist are less well-constrained than are Rayleigh wave models, suggesting it is the Love wave models that are responsible for the poor agreement in the radially anisotropic structure of the upper mantle. We have adapted the waveform inversion procedure of Debayle & Ricard to extract propagation information for the fundamental mode and up to the fifth overtone from Love waveforms in the 50-250 s period range. We have tomographically inverted these results for a mantle horizontal shear wave-speed model (β h (z)) to transition zone depths. We include azimuthal anisotropy (2θ and 4θ terms) in the tomography, but in this paper we discuss only the isotropic β h (z) structure. The data set is significantly larger, almost 500 000 Love waveforms, than previously published Love wave data sets and provides ∼17 000 000 constraints on the upper-mantle β h (z) structure. Sensitivity and resolution tests show that the horizontal resolution of the model is on the order of 800-1000 km to transition zone depths. The high wave-speed roots beneath the oldest parts of the continents appear to extend deeper for β h (z) than for β v (z) as in previous β h (z) models, but the resolution tests indicate that at least parts of these features could be artefacts. The low wave speeds beneath the mid-ocean ridges fade by ∼150 km depth except for the upper mantle beneath the East Pacific Rise which remains slow to ∼250 km depth. The resolution tests suggest that the low wave speeds at deeper depths beneath the East Pacific Rise are not solely due to vertical smearing of shallow, low wave speeds. Four prominent, low wave-speed features occur at transition zone depths-one aligned along the East African Rift, one centred south of the Indian peninsula, one located south of New Zealand and one in the south Pacific Ocean coinciding with the location of the South Pacific Superswell. The low wave-speed features south of New Zealand and south of the Indian peninsula correspond spatially with the two largest negative geoid lows on Earth.

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Section: The Regionalizationmentioning

confidence: 80%

Section: Extracting and Fitting The Secondary Observablesmentioning

confidence: 99%

Section: Extracting Structure Of the Upper Mantlementioning

confidence: 99%

Section: Extracting and Fitting The Secondary Observablesmentioning

confidence: 99%

mentioning

confidence: 99%

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A global horizontal shear velocity model of the upper mantle from multimode Love wave measurements

Ho¹,

Priestley²,

Debayle

2016

Geophys. J. Int.

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Savani: A variable resolution whole‐mantle model of anisotropic shear velocity variations based on multiple data sets

et al. 2014

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We present a tomographic model of radially anisotropic shear velocity variations in the Earth's mantle based on a new compilation of previously published data sets and a variable block parameterization, adapted to local raypath density. We employ ray-theoretical sensitivity functions to relate surface wave and body wave data with radially anisotropic velocity perturbations. Our database includes surface wave phase delays from fundamental modes up to the sixth overtone, measured at periods between 25 and 350 s, as well as cross-correlation traveltimes of major body wave phases. Before inversion, we apply crustal corrections using the crustal model CRUST2.0, and we account for azimuthal anisotropy in the upper mantle using ray-theoretical corrections based on a global model of azimuthal anisotropy. While being well correlated with earlier models at long spatial wavelength, our preferred solution, savani, additionally delineates a number of previously unidentified structures due to its improved resolution in areas of dense coverage. This is because the density of the inverse grid ranges between 1.25• in well-sampled and 5• in poorly sampled regions, allowing us to resolve regional structure better than it is typically the case in global S wave tomography. Our model highlights (i) a distinct ocean-continent anisotropic signature in the uppermost mantle, (ii) an oceanic peak in above average <1 which is shallower than in previous models and thus in better agreement with estimates of lithosphere thickness, and (iii) a long-wavelength pattern of <1 associated with the large low-shear velocity provinces in the lowermost mantle.

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Anisotropic tomography of the European lithospheric structure from surface wave studies

Nita

Maurya

Montagner

2016

Geochem Geophys Geosyst

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We present continental‐scale seismic isotropic and anisotropic imaging of shear wave upper‐mantle structure of tectonically diversified terranes creating the European continent. Taking into account the 36–200 s period range of surface waves enables us to model the deep subcontinental structure at different vertical scale‐lengths down to 300 km. After very strict quality selection criteria, we have obtained phase wave speeds at different periods for fundamental Rayleigh and Love modes from about 9000 three‐component seismograms. Dispersion measurements are performed by using Fourier‐domain waveform inversion technique named “roller‐coaster‐type” algorithm. We used the reference model with a varying average crustal structure for each source‐station path. That procedure led to significant improvement of the quality and number of phase wave speed dispersion measurements compared to the common approach of using a reference model with one average crustal structure. Surface wave dispersion data are inverted at depth for retrieving isotropy and anisotropy parameters. The fast axis directions related to azimuthal anisotropy at different depths constitute a rich database for geodynamical interpretations. Shear wave anomalies of the horizontal dimension larger than 200 km are imaged in our models. They correlate with tectonic provinces of varying age‐provenance. Different anisotropy patterns are observed along the most distinctive feature on our maps–the bordering zone between the Palaeozoic and Precambrian Europe. We discuss the depth changes of the lithosphere‐asthenosphere boundary along the profiles crossing the chosen tectonic units of different origin and age: Fennoscandia, East European Craton, Anatolia, Mediterranean subduction zones. Within the flat and stable cratonic lithosphere, we find traces of the midlithospheric discontinuity.

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A global shear velocity model of the upper mantle from fundamental and higher Rayleigh mode measurements

Cited by 100 publications

References 88 publications

A global horizontal shear velocity model of the upper mantle from multimode Love wave measurements

A global horizontal shear velocity model of the upper mantle from multimode Love wave measurements

Savani: A variable resolution whole‐mantle model of anisotropic shear velocity variations based on multiple data sets

Anisotropic tomography of the European lithospheric structure from surface wave studies

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