Waveform Tomography Reveals Channeled Flow at the Base of the Oceanic Asthenosphere

French, S. W.; Lekić, V.; Romanowicz, Barbara

doi:10.1126/science.1241514

Cited by 213 publications

(266 citation statements)

References 55 publications

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“…Wide low-wavespeed features (3-5) beneath or adjacent to regions once hypothesized to harbor narrow plume conduits are now unequivocally broad rather than smeared out, unresolved narrow features (1,2). Some early studies (25,26), using near-vertical rays, mapped broad near-vertical low-velocity regions, but these were nevertheless interpreted as "mantle plumes."…”

Section: Top-down Tectonicsmentioning

confidence: 99%

Mantle updrafts and mechanisms of oceanic volcanism

Anderson

Natland

2014

Proc. Natl. Acad. Sci. U.S.A.

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Convection in an isolated planet is characterized by narrow downwellings and broad updrafts-consequences of Archimedes' principle, the cooling required by the second law of thermodynamics, and the effect of compression on material properties. A mature cooling planet with a conductive low-viscosity core develops a thick insulating surface boundary layer with a thermal maximum, a subadiabatic interior, and a cooling highly conductive but thin boundary layer above the core. Parts of the surface layer sink into the interior, displacing older, colder material, which is entrained by spreading ridges. Magma characteristics of intraplate volcanoes are derived from within the upper boundary layer. Upper mantle features revealed by seismic tomography and that are apparently related to surface volcanoes are intrinsically broad and are not due to unresolved narrow jets. Their morphology, aspect ratio, inferred ascent rate, and temperature show that they are passively responding to downward fluxes, as appropriate for a cooling planet that is losing more heat through its surface than is being provided from its core or from radioactive heating. Response to doward flux is the inverse of the heat-pipe/mantle-plume mode of planetary cooling. Sheardriven melt extraction from the surface boundary layer explains volcanic provinces such as Yellowstone, Hawaii, and Samoa. Passive upwellings from deeper in the upper mantle feed ridges and nearridge hotspots, and others interact with the sheared and metasomatized surface layer. Normal plate tectonic processes are responsible both for plate boundary and intraplate swells and volcanism.mantle convection | geochemistry R ecent papers dealing with seismic tomography of the Earth's interior (1-3) confirm earlier studies that showed that broad upwellings, or updrafts, rather than narrow pipes, underlie or run parallel to linear volcanic chains (4-6). These wide features would have to be due to unresolved narrow (<200 km diameter) conduits if there is any validity to the mantle plume hypothesis. In addition, these hypothetical narrow conduits would have to be significantly hotter, and to be ascending at significantly greater rates, than inferred from tomographic and tectonic features and mass balance calculations. That such narrow features have not been detected is almost certainly because they do not exist and not because of poor resolution. That they do not exist can be argued from general geophysical principles, which we propose to do in this contribution. Those principles were established before plumes became the favored hypothesis of many Earth scientists for midplate volcanism. Geochemists especially did not take physical considerations into account in the formulation of their reservoir, marble cake, and whole-mantle convection models. Before considering the implications of the current tomographic state of the art, we shall briefly explain how these stark differences in opinion came about.In 1952, two influential but diametrically opposite views of the origin, evolution, and structure of...

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Section: Top-down Tectonicsmentioning

confidence: 99%

Mantle updrafts and mechanisms of oceanic volcanism

Anderson

Natland

2014

Proc. Natl. Acad. Sci. U.S.A.

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“…Zhou et al 2005;Kustowski et al 2008;Panning et al 2010;Lekić & Romanowicz 2011;French et al 2013;Auer et al 2014;Chang et al 2014;Moulik & Ekström 2014). Here, we compare our β h (z) upper-mantle model CAM2016SH with four recent β h (z) upper-mantle models: FFSW1 (Zhou et al 2005), S362ANI , SAW642ANb (Panning et al 2010) and SEMum2 (French et al 2013). The first of these is a β h (z) model whereas the later three are radial anisotropic (ξ ) model from which we have extracted the β h (z) component using the relationships between the ξ model and β h (z) given in those papers.…”

Section: O R R E L At I O N W I T H O T H E R β β H (Z) M O D E L Smentioning

confidence: 99%

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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“…The latest tool for assimilating this information into seismic velocity models is fully three-dimensional (3-D) waveform tomography [e.g., Tarantola, 1988;Tromp et al, 2005;Chen et al, 2007aChen et al, , 2007bBen Hadj Ali et al, 2009a, 2009bChen, 2011;Fichtner, 2011;Lekic and Romanowicz, 2011;Liu and Gu, 2012;Colli et al, 2013;Fichtner et al, 2013;French et al, 2013;Prieux et al, 2013;Schiemenz and Igel, 2013]. Full-3-D tomography (F3DT) accounts for the physics of wave excitation and propagation by numerically solving the inhomogeneous equations of motion for a heterogeneous, anelastic solid [Olsen et al, 1995;Komatitsch and Tromp, 1999;Cui et al, 2010;Peter et al, 2011].…”

Section: Introductionmentioning

confidence: 99%

Full‐3‐D tomography for crustal structure in Southern California based on the scattering‐integral and the adjoint‐wavefield methods

et al. 2014

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We have successfully applied full-3-D tomography (F3DT) based on a combination of the scattering-integral method (SI-F3DT) and the adjoint-wavefield method (AW-F3DT) to iteratively improve a 3-D starting model, the Southern California Earthquake Center (SCEC) Community Velocity Model version 4.0 (CVM-S4). In F3DT, the sensitivity (Fréchet) kernels are computed using numerical solutions of the 3-D elastodynamic equation and the nonlinearity of the structural inversion problem is accounted for through an iterative tomographic navigation process. More than half-a-million misfit measurements made on about 38,000 earthquake seismograms and 12,000 ambient-noise correlagrams have been assimilated into our inversion. After 26 F3DT iterations, synthetic seismograms computed using our latest model, CVM-S4.26, show substantially better fit to observed seismograms at frequencies below 0.2 Hz than those computed using our 3-D starting model CVM-S4 and the other SCEC CVM, CVM-H11.9, which was improved through 16 iterations of AW-F3DT. CVM-S4.26 has revealed strong crustal heterogeneities throughout Southern California, some of which are completely missing in CVM-S4 and CVM-H11.9 but exist in models obtained from previous crustal-scale 2-D active-source refraction tomography models. At shallow depths, our model shows strong correlation with sedimentary basins and reveals velocity contrasts across major mapped strike-slip and dip-slip faults. At middle to lower crustal depths, structural features in our model may provide new insights into regional tectonics. When combined with physics-based seismic hazard analysis tools, we expect our model to provide more accurate estimates of seismic hazards in Southern California.

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Waveform Tomography Reveals Channeled Flow at the Base of the Oceanic Asthenosphere

Cited by 213 publications

References 55 publications

Mantle updrafts and mechanisms of oceanic volcanism

Mantle updrafts and mechanisms of oceanic volcanism

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

Full‐3‐D tomography for crustal structure in Southern California based on the scattering‐integral and the adjoint‐wavefield methods

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