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Nimmo F, Faul UH, Garnero EJ. Dissipation at tidal and seismic frequencies in a melt-free Moon. ACTA ACUST UNITED AC 2012. [DOI: 10.1029/2012je004160] [Citation(s) in RCA: 43] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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Zheng Y, Lay T, Flanagan MP, Williams Q. Pervasive Seismic Wave Reflectivity and Metasomatism of the Tonga Mantle Wedge. Science 2007; 316:855-9. [PMID: 17431138 DOI: 10.1126/science.1138074] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
Subduction zones play critical roles in the recycling of oceanic lithosphere and the generation of continental crust. Seismic imaging can reveal structures associated with key dynamic processes occurring in the upper-mantle wedge above the sinking oceanic slab. Three-dimensional images of reflecting interfaces throughout the upper-mantle wedge above the subducting Tonga slab were obtained by migration of teleseismic recordings of underside P- and S-wave reflections. Laterally continuous weak reflectors with tens of kilometers of topography were detected at depths near 90, 125, 200, 250, 300, 330, 390, 410, and 450 kilometers. P- and S-wave impedances decreased at the 330-kilometer and 450-kilometer reflectors, and S-wave impedance decreased near 200 kilometers in the vicinity of the slab and near 390 kilometers, just above the global 410-kilometer increase. The pervasive seismic reflectivity results from phase transitions and compositional zonation associated with extensive metasomatism involving slab-derived fluids rising through the wedge.
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Affiliation(s)
- Yingcai Zheng
- Department of Earth and Planetary Sciences, University of California, Santa Cruz, CA 95064, USA
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Chen Y, Crittenden JC, Hackney S, Sutter L, Hand DW. Preparation of a novel TiO2-based p-n junction nanotube photocatalyst. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2005; 39:1201-1208. [PMID: 15787357 DOI: 10.1021/es049252g] [Citation(s) in RCA: 93] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
TiO2 nanotube semiconductors contain free spaces in their interior that can be filled with active materials such as chemical compounds, enzymes, and noble metals, giving them a fundamental advantage over colloids. Although the unique shape of semiconductor nanotubes makes them promising for a range of potential applications, significant developmental research is required. In this research, a novel TiO2 nanotube photocatalyst was prepared that has a p-n junction. The photocatalyst particle surface is physically divided into reduction and oxidation surfaces, which poses a potential driving force for the transport of photogenerated charge carriers. The structure of this nanotube catalyst was characterized using a scanning electron microscope (SEM) and X-ray diffraction (XRD). The catalyst activity was evaluated by coating the catalyst on HEPA filters and determining the destruction rate of toluene in air. The p-n junction nanotube catalyst was shown to have a much higher photocatalytic destruction rate than that of commercially available, nonnanotube structured material, and a higher destruction rate for nanotube catalysts that did not contain a p-n junction.
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Affiliation(s)
- Yongsheng Chen
- Department of Civil and Environmental Engineering, Arizona State University, Tempe, Arizona 85287, USA
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Debayle E, Kennett B, Priestley K. Global azimuthal seismic anisotropy and the unique plate-motion deformation of Australia. Nature 2005; 433:509-12. [PMID: 15690038 DOI: 10.1038/nature03247] [Citation(s) in RCA: 230] [Impact Index Per Article: 12.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2004] [Accepted: 11/29/2004] [Indexed: 11/08/2022]
Abstract
Differences in the thickness of the high-velocity lid underlying continents as imaged by seismic tomography, have fuelled a long debate on the origin of the 'roots' of continents. Some of these differences may be reconciled by observations of radial anisotropy between 250 and 300 km depth, with horizontally polarized shear waves travelling faster than vertically polarized ones. This azimuthally averaged anisotropy could arise from present-day deformation at the base of the plate, as has been found for shallower depths beneath ocean basins. Such deformation would also produce significant azimuthal variation, owing to the preferred alignment of highly anisotropic minerals. Here we report global observations of surface-wave azimuthal anisotropy, which indicate that only the continental portion of the Australian plate displays significant azimuthal anisotropy and strong correlation with present-day plate motion in the depth range 175-300 km. Beneath other continents, azimuthal anisotropy is only weakly correlated with plate motion and its depth location is similar to that found beneath oceans. We infer that the fast-moving Australian plate contains the only continental region with a sufficiently large deformation at its base to be transformed into azimuthal anisotropy. Simple shear leading to anisotropy with a plunging axis of symmetry may explain the smaller azimuthal anisotropy beneath other continents.
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Affiliation(s)
- Eric Debayle
- Institut de Physique du Globe de Strasbourg, Ecole et Observatoire des Sciences de la Terre, Centre National de la Recherche Scientifique and Université Louis Pasteur, 61084 Strasbourg, Cedex, France.
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Stixrude L. Mineralogy and elasticity of the oceanic upper mantle: Origin of the low-velocity zone. ACTA ACUST UNITED AC 2005. [DOI: 10.1029/2004jb002965] [Citation(s) in RCA: 212] [Impact Index Per Article: 11.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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Gung Y, Panning M, Romanowicz B. Global anisotropy and the thickness of continents. Nature 2003; 422:707-11. [PMID: 12700758 DOI: 10.1038/nature01559] [Citation(s) in RCA: 357] [Impact Index Per Article: 17.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/18/2002] [Accepted: 03/04/2003] [Indexed: 11/08/2022]
Abstract
For decades there has been a vigorous debate about the depth extent of continental roots. The analysis of heat-flow, mantle-xenolith and electrical-conductivity data all indicate that the coherent, conductive part of continental roots (the 'tectosphere') is at most 200-250 km thick. Some global seismic tomographic models agree with this estimate, but others suggest that a much thicker zone of high velocities lies beneath continental shields, reaching a depth of at least 400 km. Here we show that this disagreement can be reconciled by taking into account seismic anisotropy. We show that significant radial anisotropy, with horizontally polarized shear waves travelling faster than those that are vertically polarized, is present under most cratons in the depth range 250-400 km--similar to that found under ocean basins at shallower depths of 80-250 km. We propose that, in both cases, the anisotropy is related to shear in a low-viscosity asthenospheric channel, located at different depths under continents and oceans. The seismically defined 'tectosphere' is then at most 200-250 km thick under old continents. The 'Lehmann discontinuity', observed mostly under continents at about 200-250 km, and the 'Gutenberg discontinuity', observed under oceans at depths of about 60-80 km, may both be associated with the bottom of the lithosphere, marking a transition to flow-induced asthenospheric anisotropy.
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Affiliation(s)
- Yuancheng Gung
- Berkeley Seismological Laboratory and Department of Earth and Planetary Science, Berkeley, California 94720, USA
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Saul J, Vinnik L. Earth science: Mantle deformation or processing artefact? Nature 2003; 422:136; discussion 136. [PMID: 12634776 DOI: 10.1038/422136a] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Affiliation(s)
- Joachim Saul
- GeoForschungsZentrum Potsdam, Telegrafenberg, 14473 Potsdam, Germany.
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Hirth G, Kohlstedt D. Rheology of the upper mantle and the mantle wedge: A view from the experimentalists. INSIDE THE SUBDUCTION FACTORY 2003. [DOI: 10.1029/138gm06] [Citation(s) in RCA: 634] [Impact Index Per Article: 30.2] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/04/2022]
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Abstract
Elastic anisotropy is present where the speed of a seismic wave depends on its direction. In Earth's mantle, elastic anisotropy is induced by minerals that are preferentially oriented in a directional flow or deformation. Earthquakes generate two seismic wave types: compressional (P) and shear (S) waves, whose coupling in anisotropic rocks leads to scattering, birefringence, and waves with hybrid polarizations. This varied behavior is helping geophysicists explore rock textures within Earth's mantle and crust, map present-day upper-mantle convection, and study the formation of lithospheric plates and the accretion of continents in Earth history.
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Affiliation(s)
- Jeffrey Park
- Department of Geology and Geophysics, Yale University, Post Office Box 208109, New Haven, CT 06520-8109, USA
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Wookey J, Kendall JM, Barruol G. Mid-mantle deformation inferred from seismic anisotropy. Nature 2002; 415:777-80. [PMID: 11845205 DOI: 10.1038/415777a] [Citation(s) in RCA: 136] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
With time, convective processes in the Earth's mantle will tend to align crystals, grains and inclusions. This mantle fabric is detectable seismologically, as it produces an anisotropy in material properties--in particular, a directional dependence in seismic-wave velocity. This alignment is enhanced at the boundaries of the mantle where there are rapid changes in the direction and magnitude of mantle flow, and therefore most observations of anisotropy are confined to the uppermost mantle or lithosphere and the lowermost-mantle analogue of the lithosphere, the D" region. Here we present evidence from shear-wave splitting measurements for mid-mantle anisotropy in the vicinity of the 660-km discontinuity, the boundary between the upper and lower mantle. Deep-focus earthquakes in the Tonga-Kermadec and New Hebrides subduction zones recorded at Australian seismograph stations record some of the largest values of shear-wave splitting hitherto reported. The results suggest that, at least locally, there may exist a mid-mantle boundary layer, which could indicate the impediment of flow between the upper and lower mantle in this region.
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Affiliation(s)
- James Wookey
- School of Earth Sciences, University of Leeds, Woodhouse Lane, Leeds LS2 9JT, UK
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Debayle E, Kennett BLN. The Australian continental upper mantle: Structure and deformation inferred from surface waves. ACTA ACUST UNITED AC 2000. [DOI: 10.1029/2000jb900212] [Citation(s) in RCA: 165] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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Solomatov VS, Moresi LN. Scaling of time-dependent stagnant lid convection: Application to small-scale convection on Earth and other terrestrial planets. ACTA ACUST UNITED AC 2000. [DOI: 10.1029/2000jb900197] [Citation(s) in RCA: 273] [Impact Index Per Article: 11.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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Fouch MJ, Fischer KM, Parmentier EM, Wysession ME, Clarke TJ. Shear wave splitting, continental keels, and patterns of mantle flow. ACTA ACUST UNITED AC 2000. [DOI: 10.1029/1999jb900372] [Citation(s) in RCA: 200] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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Mainprice D, Barruol G, Ismaïl WB. The Seismic anisotropy of the Earth's mantle: From single crystal to polycrystal. EARTH'S DEEP INTERIOR: MINERAL PHYSICS AND TOMOGRAPHY FROM THE ATOMIC TO THE GLOBAL SCALE 2000. [DOI: 10.1029/gm117p0237] [Citation(s) in RCA: 143] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/03/2022]
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Katzman R, Zhao L, Jordan TH. High-resolution, two-dimensional vertical tomography of the central Pacific mantle usingScSreverberations and frequency-dependent travel times. ACTA ACUST UNITED AC 1998. [DOI: 10.1029/98jb00504] [Citation(s) in RCA: 87] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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Upper mantle structure beneath Australia from portable array deployments. ACTA ACUST UNITED AC 1998. [DOI: 10.1029/gd026p0039] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/12/2023]
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Clitheroe G, van der Hilst R. Complex anisotropy in the Australian lithosphere from shear-wave splitting in broad-band SKS Records. STRUCTURE AND EVOLUTION OF THE AUSTRALIAN CONTINENT 1998. [DOI: 10.1029/gd026p0073] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
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Davis P, England P, Houseman G. Comparison of shear wave splitting and finite strain from the India-Asia collision zone. ACTA ACUST UNITED AC 1997. [DOI: 10.1029/97jb02378] [Citation(s) in RCA: 42] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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Barruol G, Silver PG, Vauchez A. Seismic anisotropy in the eastern United States: Deep structure of a complex continental plate. ACTA ACUST UNITED AC 1997. [DOI: 10.1029/96jb03800] [Citation(s) in RCA: 147] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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Dueker KG, Sheehan AF. Mantle discontinuity structure from midpoint stacks of converted P to S waves across the Yellowstone hotspot track. ACTA ACUST UNITED AC 1997. [DOI: 10.1029/96jb03857] [Citation(s) in RCA: 356] [Impact Index Per Article: 13.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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Thybo H, Perchuc E. The Seismic 8degrees Discontinuity and Partial Melting in Continental Mantle. Science 1997; 275:1626-9. [PMID: 9054353 DOI: 10.1126/science.275.5306.1626] [Citation(s) in RCA: 206] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
Strong, scattered reflections beyond 8 degrees (8degrees) offset are characteristic features of all high-resolution seismic sections from the continents. The reflections identify a low-velocity zone below approximately 100 kilometers depth beneath generally stratified mantle. This zone may be caused by partial melting, globally initiated at equal depth in the continental mantle. Solid state is again attained at the Lehmann discontinuity in cold, stable areas, whereas the zone extends to near the 400-kilometer discontinuity in hot, tectonically active areas. Thus, the depth to the Lehmann discontinuity may be an indicator of the thermal state of the continental mantle.
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Affiliation(s)
- H Thybo
- H. Thybo, Geological Institute, University of Copenhagen, Oster Voldgade 10, DK-1350 Copenhagen K, Denmark. E. Perchuc, Institute of Geophysics, Polish Academy of Sciences, ul.Ksiecia Janusza 64, PL-01452 Warsaw, Poland
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Gaherty JB, Jordan TH, Gee LS. Seismic structure of the upper mantle in a central Pacific corridor. ACTA ACUST UNITED AC 1996. [DOI: 10.1029/96jb01882] [Citation(s) in RCA: 145] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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Fouch MJ, Fischer KM. Mantle anisotropy beneath northwest Pacific subduction zones. ACTA ACUST UNITED AC 1996. [DOI: 10.1029/96jb00881] [Citation(s) in RCA: 165] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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