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Seismic polarization anisotropy beneath the central Tibetan Plateau

Authors

Huang,  W. C.
External Organizations;
Publikationen aller GIPP-unterstützten Projekte, Deutsches GeoForschungsZentrum;
GEOFON, Deutsches GeoForschungsZentrum;

Ni,  J. F.
External Organizations;
Publikationen aller GIPP-unterstützten Projekte, Deutsches GeoForschungsZentrum;
GEOFON, Deutsches GeoForschungsZentrum;

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Tilmann,  Frederik
2.4 Seismology, 2.0 Physics of the Earth, Departments, GFZ Publication Database, Deutsches GeoForschungsZentrum;
Publikationen aller GIPP-unterstützten Projekte, Deutsches GeoForschungsZentrum;
GEOFON, Deutsches GeoForschungsZentrum;

Nelson,  D.
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Publikationen aller GIPP-unterstützten Projekte, Deutsches GeoForschungsZentrum;
GEOFON, Deutsches GeoForschungsZentrum;

Guo,  J.
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Publikationen aller GIPP-unterstützten Projekte, Deutsches GeoForschungsZentrum;
GEOFON, Deutsches GeoForschungsZentrum;

Zhao,  W.
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Publikationen aller GIPP-unterstützten Projekte, Deutsches GeoForschungsZentrum;
GEOFON, Deutsches GeoForschungsZentrum;

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Mechie,  James
2.2 Geophysical Deep Sounding, 2.0 Physics of the Earth, Departments, GFZ Publication Database, Deutsches GeoForschungsZentrum;
Publikationen aller GIPP-unterstützten Projekte, Deutsches GeoForschungsZentrum;
GEOFON, Deutsches GeoForschungsZentrum;

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Kind,  Rainer
2.4 Seismology, 2.0 Physics of the Earth, Departments, GFZ Publication Database, Deutsches GeoForschungsZentrum;
Publikationen aller GIPP-unterstützten Projekte, Deutsches GeoForschungsZentrum;
GEOFON, Deutsches GeoForschungsZentrum;

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Saul,  Joachim
2.4 Seismology, 2.0 Physics of the Earth, Departments, GFZ Publication Database, Deutsches GeoForschungsZentrum;
Publikationen aller GIPP-unterstützten Projekte, Deutsches GeoForschungsZentrum;
GEOFON, Deutsches GeoForschungsZentrum;

Rapine,  R.
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Publikationen aller GIPP-unterstützten Projekte, Deutsches GeoForschungsZentrum;
GEOFON, Deutsches GeoForschungsZentrum;

Hearn,  T. M.
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Publikationen aller GIPP-unterstützten Projekte, Deutsches GeoForschungsZentrum;
GEOFON, Deutsches GeoForschungsZentrum;

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Citation

Huang, W. C., Ni, J. F., Tilmann, F., Nelson, D., Guo, J., Zhao, W., Mechie, J., Kind, R., Saul, J., Rapine, R., Hearn, T. M. (2000): Seismic polarization anisotropy beneath the central Tibetan Plateau. - Journal of Geophysical Research, 105, B12, 27979-27989.
https://doi.org/10.1029/2000JB900339


Cite as: https://gfzpublic.gfz-potsdam.de/pubman/item/item_227755
Abstract
SKS and SKKS shear waves recorded on the INDEPTH III seismic array deployed in central Tibet during 1998 - 1999 have been analysed for the direction and extent of seismic polarization anisotropy. The 400-km-long NNW trending array extended south to north, from the central Lhasa terrane, across the Karakoram-Jiali fault system and Banggong-Nujiang suture to the central Qiangtang terrane. Substantial splitting with delay times from 1 to 2 s, and fast directions varying from E-W to NE-SW, was observed for stations in the Qiangtang trerrane and northernmost Lhasa terrane. No detectable splitting was observed for stations located farther south in the central Lahsa terrane. The change in shear wave splitting characteristics occurs at 32°N, approximately coincident with the transcurrent Karakoram-Jiali fault system but ~40 km south of the surface trace of the Banggong-Nujiang suture. This location is also near the southernmost edge of a region of high Sn attenuation and low upper mantle velocities found in previous studies. The transition between no measured splitting and strong anisotropy (2.2 s delay time) is exceptionally sharp (=15 km), suggesting a large crustal contribution to the measured splitting. The E-W to NE-SW fast directions are broadly similar to the fast directions observed farther east along the Yadong-Golmud highway, suggesting that no large-scale change in anisotropic properties occurs in the east-west direction. However, in detail, fast directions and delay times vary over lateral distances of ~100 km in both the N-S and E-W direction by as much as 40° and 0.5-1 s, respectively. The onset of measurable splitting at 32° N most likely marks the northern limit of the underthrusting Indian lithosphere, which is characterized by negligible polarization anisotropy. Taken in conjunction with decades of geophysical and geological observations in Tibet, the new anisotropy measurements are consistent with a model where hot and weak upper mantle beneath northern Tibet is being squeezed and sheared between the advancing Indian lithosphere to the south and the Tsaidam and Tarim Lithospheres to the north and west, resulting in eastward flow and possibly thickening and subsequent detachment due to gravitational instability. In northern Tibet, crustal deformation clearly follows this large-scale deformation pattern.