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  • 1
    GFZ publications
    GFZ publications
    High resolution 3D Rayleigh wave velocity model of China and surrounding area (2013)
    Potsdam : Deutsches GeoForschungsZentrum
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    Call number: 21/STR 13/01
    In: Scientific technical report
    Type of Medium: GFZ publications
    Pages: 197 S.
    Series Statement: Scientific technical report / Deutsches GeoForschungsZentrum GFZ 13/01
    URL: http://ebooks.gfz-potsdam.de/pubman/item/escidoc:104130
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  • 2
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    Crustal Structure Around the Tristan da Cunha Hotspot Derived from Ambient Noise (2015)
    In:  EPIC3AGU Fall Meeting, San Francisco, USA, 2015-12-14-2015-12-18
    Details
    Publication Date: 2016-02-07
    Description: According to classical plume theory, the Tristan da Cunha hotspot is thought to have played a major role in the rifting of the South Atlantic margins and the creation of the aseismic Walvis Ridge during and after the breakup of the South Atlantic. Between February 2012 and January 2013 a network of 24 broadband ocean-bottom seismometers was in operation around the volcanic archipelago of Tristan da Cunha. Ambient noise data from the OBS and a seismic station on Nightingale Island were used to constrain the crustal and uppermost structure around the island. From the vertical and hydrophone recordings of more than 300 days we could reconstruct the ambient noise Green's functions by cross-correlation. The dispersion curves of Rayleigh/Scholte waves could be derived from the cross-correlations in the period range from 2 to 32 seconds. Group velocity maps were determined for each individual period using travel time tomography. These group velocity maps were converted to depth by dispersion curve inversion to construct a 3D S-wave velocity model of the crust and uppermost mantle in the region. This model shows a strong velocity anomaly beneath the Tristan da Cunha archipelago. The influence of the water depth on the inversion is discussed.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , notRev
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  • 3
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    A 3D shear-wave velocity model of the upper mantle beneath China and the surrounding areas (2014)
    Elsevier
    In:  EPIC3Tectonophysics, Elsevier, 633, pp. 193-210, ISSN: 0040-1951
    Details
    Publication Date: 2014-12-02
    Description: We present a three-dimensional model of shear wave velocity for the upper mantle of China and the surrounding region by analyzing 50,338 vertical component multi-mode Rayleigh wave seismograms, recorded at 144 permanent and more than 300 temporary broadband stations in and around China. The procedure involves combination of 1-D path average models obtained by modeling each Rayleigh waveform up to the 4th higher mode in a tomographic inversion scheme. The dense station network and the use of multi-mode analysis help to achieve a lateral resolution of a few hundred kilometers down to 400 km depth. The seismic lithosphere, as it is defined by the crust and the high velocity mantle lid, is to the first order thin in east China and thick in the west, with a high velocity lid extending down to about 200 km depth beneath much of the Tibet–Pamir plateau. Beneath India, the thickness of the seismic lithosphere gradually increases from ~ 100 km in south India to more than 150 km in north India, where it underthrusts the Tibetan plateau to approximately the Jinsha River Suture. High velocity lid extending down to 100–150 km depth is also observed in the Tarim basin, Sichuan basin and Ordos block. In the eastern part of the North China craton the seismic lithosphere is probably close to or thinner than 70 km. Adjacent to these areas, the high velocity lid in the eastern Yangtze craton and South China fold system extends down to 70–80 km depth. A large-scale subhorizontal high velocity body is observed at depths of 150–350 km beneath the entire east China cratonic areas. This high velocity body might be the remnant of a delamination process which resulted in the decratonization of the North China and the Yangtze cratons.
    Repository Name: EPIC Alfred Wegener Institut
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  • 4
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    Insight into the shallow lithosphere structure and magmatic plumbing system beneath the Tristan da Cunha hot spot from geophysical and petrological studies (2015)
    Mineralogical Society of Poland
    In:  EPIC32nd European Mantle Workshop, Wroclaw, Poland, 2015-08-25-2015-08-28Mineralogia - Special Papers, 43, p. 41, Mineralogical Society of Poland
    Details
    Publication Date: 2016-01-21
    Description: According to classical plume theory, the Tristan da Cunha plume is thought to have played a major role in the rifting of the South Atlantic margins and the creation of the aseismic Walvis Ridge by impinging at the base of the continental lithosphere shortly before or during the breakup of the South Atlantic margins. However, Tristan da Cunha is enigmatic as it cannot be clearly identified as a deep-rooted hot spot, but may instead be related to a more shallow feature in the mantle that could actually have been caused by the opening of the South Atlantic. The equivocal character of Tristan da Cunha is largely due to a lack of geophysical and petrological data in this region. We therefore staged a multi-disciplinary geophysical study of the region by acquiring passive marine electromagnetic and seismic data, and bathymetric data within the framework of the SPP1375 South Atlantic Margin Processes and Links with onshore Evolution (SAMPLE) funded by the German Science foundation. The experiment included two expeditions onboard the German R/V MARIA S. MERIAN in 2012 and 2013. In addition to the geophysical work, a landing party collected samples for petrological studies. In our contribution we present first results on the shallow lithosphere structure beneath the Tristan da Cunha archipelago derived from geophysical studies. These results are combined with results from thermobarometric analyses of basanitic/ankaramitic rocks that represent the main rock type on the island. The more evolved products of the eruption in 1962, (trachyandesites), were also studied to include the full range of magma compositions. Clinopyroxene-melt thermobarometry yielded crystallization pressures between 4 and 14 kbar, corresponding to depths of 12-42 km, whereby the youngest and most evolved rocks erupted from the shallowest depth. Olivine-, clinopyroxene-, and plagioclase-melt thermometry yielded magmatic temperatures of 1100° - 1320°C. The Moho below the archipelago is at approximately 11-12 km depth based on the receiver function method at two island stations and ocean-bottom seismometers. Therefore the petrologic depth estimates demonstrate that magmas erupted from a plumbing system in the uppermost mantle.
    Repository Name: EPIC Alfred Wegener Institut
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  • 5
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    Crustal Structure Around the Tristan da Cunha Hotspot Derived from Ambient Noise (2016)
    In:  EPIC3EGU General Assembly 2016, Vienna, 2016-04-17-2016-04-22Geophysical Research Abstracts Vol. 18, EGU2016-13841
    Details
    Publication Date: 2016-01-21
    Description: According to classical plume theory, the Tristan da Cunha hotspot is thought to have played a major role in the rifting of the South Atlantic margins and the creation of the aseismic Walvis Ridge during and after the breakup of the South Atlantic. Between February 2012 and January 2013 a network of 24 broadband ocean-bottom seismometers was in operation around the volcanic archipelago of Tristan da Cunha. Ambient noise data from the OBS and a seismic station on Nightingale Island were used to constrain the crustal and uppermost structure around the island. From the vertical and hydrophone recordings of more than 300 days we could reconstruct the ambient noise Green's functions by cross-correlation. The dispersion curves of Rayleigh/Scholte waves could be derived from the cross-correlations in the period range from 2 to 32 seconds. Group velocity maps were determined for each individual period using travel time tomography. These group velocity maps were converted to depth by dispersion curve inversion to construct a 3D S-wave velocity model of the crust and uppermost mantle in the region. This model shows a strong velocity anomaly beneath the Tristan da Cunha archipelago. The influence of the water depth on the inversion is discussed.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , notRev
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  • 6
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    Structure of the Crust and Mantle Lithosphere underneath NW Namibia Revealed by the WALPASS Seismic Experiment (2013)
    In:  EPIC3American Geophysical Union, Fall Meeting 2013, 2013-12-09-2013-12-13AGU Fall Meeting Abstracts, pp. G2678
    Details
    Publication Date: 2014-12-11
    Description: The amphibian Walvis Ridge Passive-Source Seismic Experiment (WALPASS) have been operated for a period of two years from 2010 to 2012 in the area where the Walvis Ridge intersects the continental margin of northwestern Namibia. The deployment was intended to study the lithospheric and upper mantle structure in the ocean-continent transition area beneath the passive continental margin. The main idea is to find seismic anomalies related to the postulated hotspot track from the continent to the ocean along the Walvis Ridge that links the Etendeka continental flood-basalt province to the Tristan da Cunha hotspot in the mid Atlantic ocean. This could provide clues of the role of plume-lithosphere interaction during the continental break-up. We present here seismic structures of the crustal and mantle lithosphere in this geophysically little studied region using seismic methods including P and S receiver functions and shear wave splitting. The average crustal thickness in the continental Namibia is ~35 km with a relatively low Vp/Vs ratio of 1.7. Underneath the NE extension of the Walvis Ridge the crust is the thickest (45 km) with a high Vp/Vs ratio (〉1.80). The thick crust and high Vp/Vs ratio beneath the Walvis Ridge are consistent with high Vp derived by controlled source seismics, implying a magmatic underplating. A low velocity zone in the mantle is observed at depths of 60-120 km, possibly representing the base of the lithosphere. The P-to-S converted phases at the 410 and 660 km discontinuities arrive 2-3 s earlier, indicating higher upper mantle velocities (+5%). Seismic anisotropy in the mantle derived by the SKS splitting exhibits a pattern of the plume and plate interaction.
    Repository Name: EPIC Alfred Wegener Institut
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  • 7
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    Status of the surface wave analysis for WALPASS dataset (2014)
    In:  EPIC3SAMPLE Workshop, Bremerhaven, 2014-06-03-2014-06-06
    Details
    Publication Date: 2014-12-04
    Description: The Walvis Ridge is the connecting link between the Tristan da Cunha hotspot and the Etendeka continental flood basalt province. This is an ideal location to get a better understanding for the plume-lithosphere interaction and the breakup of the continents. In the midst of the controversial topic of the likes of plume theory and various deep-Earth processes it is essential to have a clear image of this region to put forward any kind of geodynamical model. Within the frame of the WALPASS project twelve broadband ocean-bottom seismometer (BBOBS) had been deployed off the north-west coast of Namibia. as well as 28 land stations in northwestern Namibia. The seismological net covers an area of approximately 400 x 800 km. Data from eleven months (BBOBS) and up to two years (land stations) are available. We are presenting some preliminary work done on the BBOBS data set. Due to problems with internal power of the instruments, the internal clock drift could be measured at only two stations. We test ambient noise correlation to estimate the clock drift for the remaining 10 seafloor instruments. Furthermore, we will outline following steps of analyses of ambient noise and surface waves.
    Repository Name: EPIC Alfred Wegener Institut
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  • 8
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    Uppermost mantle and crustal structure at Tristan da Cunha derived from ambient seismic noise (2017)
    ELSEVIER SCIENCE BV
    In:  EPIC3Earth and Planetary Science Letters, ELSEVIER SCIENCE BV, 471, pp. 117-124, ISSN: 0012-821X
    Details
    Publication Date: 2017-05-29
    Description: According to classical plume theory, the Tristan da Cunha hotspot, located ∼400 km east off the Mid-Atlantic Ridge, is thought to have played a major role in the rifting while creating an aseismic Walvis Ridge during and after the breakup of the South Atlantic margins. Volcanic activity on the Tristan da Cunha Island shows that the hotspot might still be there influencing the upper mantle and crustal structure. In this study we present ambient noise data from 24 broadband OBS around Tristan da Cunha and a seismic station on Nightingale Island, which provide first constraints on the crustal and uppermost mantle structure around the island. By combining ambient noise techniques, dispersion curve analysis of Rayleigh waves, 2D tomographic inversion of travel times and 3D depth inversion of dispersion data we derived a 3D VSvelocity model around the archipelago of Tristan da Cunha. The model shows an isolated, vertically sharp bounded thickened and modified crust beneath the islands surrounded by thin oceanic crust (〈5 km). The velocity anomaly shows a typical volcanic structure with a shallow high velocity body and a low velocity root reaching into the upper mantle, which we interpret as shallow solidified magmatic material and volcanic feeding system/magmatic underplating, respectively. The observed simple and localized volcanic structure, embedded in a rather homogeneous crust and upper mantle indicates only minor and very localized magmatic overprinting of the existing lithosphere by the Tristan da Cunha hotspot. The uppermost mantle S wave velocity beneath nearby seamounts and to the SW of the islands is also slow and could indicate a thermal influence from a deeper source, whereas the Tristan da Cunha Fracture Zone shows no signs of modification.
    Repository Name: EPIC Alfred Wegener Institut
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  • 9
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    Depth-variant azimuthal anisotropy in Tibet revealed by surface wave tomography (2015)
    Wiley
    In:  EPIC3Geophysical Research Letters, Wiley, 42(11), pp. 4326-4334, ISSN: 0094-8276
    Details
    Publication Date: 2015-08-09
    Description: Azimuthal anisotropy derived from multi-mode Rayleigh wave tomography in China exhibits depth-dependent variations in Tibet, which can be explained as induced by the Cenozoic India-Eurasian collision. In west Tibet, the E-W fast polarization direction at depths 〈100 km is consistent with the accumulated shear strain in the Tibetan lithosphere, whereas the N-S fast direction at greater depths is aligned with Indian plate motion. In northeast Tibet, depth-consistent NW-SE directions imply coupled deformation throughout the whole lithosphere, possibly also involving the underlying asthenosphere. Significant anisotropy at depths of 225 km in southeast Tibet reflects sublithospheric deformation induced by northward and eastward lithospheric subduction beneath the Himalaya and Burma, respectively. The multi-layer anisotropic surface wave model can explain some features of SKS splitting measurements in Tibet, with differences probably attributable to the limited backazimuthal coverage of most SKS studies in Tibet and the limited horizontal resolution of the surface wave results.
    Repository Name: EPIC Alfred Wegener Institut
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  • 10
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    The Tristan da Cunha mantle plume and its role in the continental breakup and opening of the South Atlantic Ocean (2019)
    In:  EPIC3Geo-Kolloquium, TU Bergakademie Freiberg, 2019-05-22-2019-05-22
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    Publication Date: 2020-04-12
    Repository Name: EPIC Alfred Wegener Institut
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