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| Titel |
Toward developing a 3D seismic velocity model beneath the SE Tibetan and surrounding regions |
| VerfasserIn |
Ya Sun, Jianxin Liu, Fenglin Niu |
| Konferenz |
EGU General Assembly 2014
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250086441
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| Publikation (Nr.) |
 EGU/EGU2014-309.pdf |
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| Zusammenfassung |
| We investigated crustal and lithospheric mantle seismic structure beneath the southeast
of the Tibetan plateau and the surrounding regions to understand what roles the lower
crust and lithospheric mantle have played in shaping area. Firstly, we analyzed receiver
function data that were recorded by four provincial seismic networks of the China
Earthquake Administration, comprising of 88 broadband stations in the study area,
from earthquakes occurring from July 2007 to July 2010. We have employed a new
analysis technique for estimating crustal anisotropy and found significant seismic
anisotropy with the splitting time of 0.3-0.8s beneath the SE margin of the
Tibetan plateau. Both the splitting time and the fast direction were comparable
to the result from the SKS/SKKS data, suggesting that crustal anisotropy is
the main cause of shear wave splitting of the SKS/SKKS wave. On the other
hand, stations located within the surrounding regions, Sichuan, Guizhou and
Yunnan showed very little or no crustal anisotropy. However, SKS splitting data
showed a sharp change of fast direction from NS in the north to EW in the south
between 27°N and 25°N near the YuiGui plateau. This sharp transition was not
observed from our crustal anisotropic result, suggesting that the crust and
lithospheric mantle have different deformation pattern in this area. Secondly, we
applied the finite frequency tomography method to map the upper mantle
tomography beneath SE Tibetan plateau, the image show some fast S wave
velocity anomalies beneath the SE margin of Tibet with the depth varying
from ~90km to 350km, which also identified the decoupled structure between
lower crust and lithospheric mantle beneath the SE Tibet margin. Once the
crustal anisotropic fast polarization direction was identified, we applied the H-k
analysis to determine the crustal thickness and two Vp/Vs ratios corresponding
to the fast and slow propagating directions. We found significant difference
between the plateau and the surrounding regions in both Moho depth and
Vp/Vs ratio. The Tibetan plateau and the western Sichuan basin showed a
higher Vp/Vs (~1.78) ratio than its southern neighbor, the Yungui plateau
(~1.68), indicating that mafic lower crustal materials composes a significant
part of the crust beneath the SE margin and some felsic or rocks that have
high SiO2 content composition in the Yun-Gui plateau. The uplifting of the
Tibetan plateau may not only be caused by the lower crustal flow, but might also
be caused by the partial lithosphere detachment. Suggesting that there are
two or more than two geodynamic models worked on the SE Tibetan plateau. |
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