Advertisement

Acta Seismologica Sinica

, Volume 9, Issue 2, pp 279–287 | Cite as

Seismic anisotropy beneath Southern Tibet

  • Qing-Tian Lü
  • Kai-Yi Ma
  • Mei Jiang
  • A. Hirn
  • A. Nercessian
Article

Abstract

We have examined shear-wave splitting in teleseismic waves (SKS) recorded on 20 seismographs deployed on a profile that followed the Southern Tibet highway during the 1992 Sino-French seismic experiment. The “cross-correlation” method is applied to derive splitting parameters. The most striking feature is the abrupt variation in splitting orientation across ITS. North of ITS, 12 stations have an average N70°E orientation of the fast wave, with a delay between the fast and slow waves of up to 1 second. On the contrary, 7 stations located to the south of ITS show an N25°W orientation and a smaller magnitude. We compare the observations with surface geological features and discuss the source of anisotropy and its constraints on the deformation model of the Tibetan Plateau. Our studies suggest that the anisotropy may be generated by the high strain induced by the underthrusting of the India lithosphere in the south of ITS. North of ITS, anisotropy may relate to ductile deformation and flow in the upper mantle. Analysis of the anisotropy pattern with the deformation models of the Tibetan Plateau suggests that both internal ductile deformation and continental northeastward extrusion contribute to crustal shortening and uplift of the Tibetan Plateau.

Key words

Tibetan Plateau anisotropy shear-wave splitting upper mantle 

Preview

Unable to display preview. Download preview PDF.

Unable to display preview. Download preview PDF.

References

  1. Argand, E., La tectonique de L’asie, 1924.Int. Geol., Congr., 13th,7: 171–372.Google Scholar
  2. Avouac, J. P. and Tapponnier, P., 1993. Kinematic model of active deformation in central Asia.Geophys. Res. Lett.,20 (10): 895–898.Google Scholar
  3. Barazangi, M. and Ni, J., 1982. Velocities and propagation characteristics of Pn and Sn beneath the Himalayan arc and Tibetan Plateau; Possible evidence for underthrusting of the Indian continental lithosphere beneath Tibet.Geology,10: 179–185.CrossRefGoogle Scholar
  4. Bowman, J. R. and Ando, M., 1987. Shear-wave splitting in the upper-mantle wedge above the Tonga subduction zone.Geophys. J. R. astr. Soc.,88: 25–41.Google Scholar
  5. Chen, G. Y. and Zeng, R. S., 1985. The difference of lithospheric structure between Himalayan mountain and Tibetan Plateau from surface wave dispersion.Acta Geophysica Sinica,28, Supplement I: 161–173 (in Chinese).Google Scholar
  6. Chen, W. P. and Molnar, P., 1981. Constraints on seismic wave velocity structure beneath the Tibetan Plateau and their tectonic implication.J. Geophys. Res,86: 5937–5962.Google Scholar
  7. Crampin, S., 1978. Seismic wave propagation through a cracked solid: polarization as a possible dilatancy diagnostic.Geophys. J. R. astr. Soc.,53: 467–496.Google Scholar
  8. Crampin, S., 1981. A review of wave motion in anisotropic and cracked elastic-media.Wave Motion,3: 343–391.CrossRefGoogle Scholar
  9. Dewey, J. F., Shackleton, R. M. and Chang, C. F.et al., 1988. The tectonic evolution of the Tibetan Plateau.Phil. Trans. R. Soc. Lond.,A327, 379–413.CrossRefGoogle Scholar
  10. England, P., and Houseman, G., 1989. Extension during continental convergence, with application to the Tibetan Plateau.J. Geophys. Res.,94: 17 561–17 579.Google Scholar
  11. Houseman, G. A., Mckenzie, D. P. and Molnar, P., 1981. Convective instability of a thickened boundary layer and its relavance for the thermal evolution of continental convergence belts.J. Geophys. Res.,86: 6115–6132.Google Scholar
  12. Jiang, M., Lu, Q. T. and Xue, G. Q., 1994. Researchs on the crustal structures of the Tibetan Plateau by means of seismic experiment jointly conducted by Chinese and French geophysicists.Acta Geophysica Sinica,37(3): 412–413 (in Chinese).Google Scholar
  13. Kumazawa, M. and Anderson, O.L., 1969. Elastic moduli, pressure derivatives, and temperature derivatives of single-crystal olivine and single-crystal for sterite.J. Geophys. Res.,74: 5961–5972.Google Scholar
  14. Wu, G. J., Gao, R. and Yu, Q. F.,et al., 1991. Integrated investigations of the Qinghai-Tibet Plateau along the Yadong-Golmud geoscience transect.Acta Geophysica Sinica,34(5): 552–562 (in Chinese).Google Scholar
  15. Lu, Q. T., 1993. Field method for Lithospheric detection in Tibetan Plateau.Foreign Geoexploration Technology,6: 8–10 (in Chinese).Google Scholar
  16. Mc Namara, D. E., Owens, T. J. and Silver, P. G.,et al., 1994. Shear wave anisotropy beneath the Tibetan Plateau.J. Geophys. Res.,99: 13 655–13 665.CrossRefGoogle Scholar
  17. Molnar, P. and Tapponnier, T., 1975. Cenozoic tectonics of Asia: Effects of a continental collision.Science,189: 419–426.CrossRefGoogle Scholar
  18. Makeyeva, L. I., Vinnik, L. P. and Roecker, S. W., 1992. Shear-wave splitting and small-scale convection in the continental upper mantle.Nature,358: 144–146.CrossRefGoogle Scholar
  19. Nicolas, A. and Christense, N. I., 1987. Formation of anisotropy in upper mantle peridotites — A review, In:Composition, Structure and Dynamics of the Lithosphere — Asthenosphere system, K. Fuchs and C. Froidevanx (eds),Geodyn. Ser. AGU,16: 111–123.Google Scholar
  20. Patria, P. and Achache, J., 1984. India-Eurasia collision chronology has implications for crustal shortening and driving mechanism of plates.Nature,311: 615–621.CrossRefGoogle Scholar
  21. Peltzer, G. and Tapponnier, P., 1988. Formation and evolution of strike-slip faults, rifts, and basins during the India-Asia collision: An experimental approach.J. Geophys. Res.,93: 15 085–15 117.Google Scholar
  22. Ribe, N. M., 1989. Seismic anistropy and mantle flow.J. Geophy. Res.,94: 4213–4223.Google Scholar
  23. Ribe, N. M., 1992. On the relation between seismic anisotropy and finite strain.J. Geophys. Res.,97: 8 737–8 747.Google Scholar
  24. Shih, X. R., Meyer, R. P. and Schneider, J. F., 1989. An automated analytic method to determin shear-wave anisotropy.Tectomophysics,165: 271–278.CrossRefGoogle Scholar
  25. Silver, P. G. and Chan, W. W., 1988. Implications for continental structure and evolution from seismic anisotropy.Nature,335: 34–39.CrossRefGoogle Scholar
  26. Silver, P. G. and Chan, W. W., 1991. Shear wave splitting and subcontinental mantle deformation.J. Geophys. Res.,96: 16 429–16 454.CrossRefGoogle Scholar
  27. Silver, P. G., Kaneshima, and Meade, C., 1993. Why is the lower mantle so isotropic?Eos, Trans. Amer. Geophys. Un., 74.Google Scholar
  28. Sun, K. Z. and Teng, J. W., 1985. The velocity distribution in the crust and upper mantle beneath the Tibetan Plateau from long period surface waves.Acta Geophysica Sinica,28, Supplement I: 43–53 (in Chinese).Google Scholar
  29. Tapponnier, P., Peltzer, G. and LeDain, A. Y.et al., 1982. Propagating extrusion tectonics in Asia: New insights from simple experiments with plasticine.Geology,10: 611–616.CrossRefGoogle Scholar
  30. Vinnik, L. P., Farra, V. and Romanowicz, B., 1989. Azimuthal anisotropy in the earth from observations of SKS at GEO-SCOPE and NARS broadband stations.Bull. Seism. Soc. Amer.,79: 1542–1558.Google Scholar
  31. Vinnik, L. P., Makeyeva, L. I. and Milev, A., 1992. Global patterns of azimuthal anisotropy and deformations in the continental mantle.Geophys. J. Int.,111: 433–447.CrossRefGoogle Scholar

Copyright information

© Acta Seismologica Sinica 1996

Authors and Affiliations

  • Qing-Tian Lü
    • 1
  • Kai-Yi Ma
    • 1
  • Mei Jiang
    • 1
  • A. Hirn
    • 2
  • A. Nercessian
    • 2
  1. 1.Institute of Mineral DepositsCAGSBeijingChina
  2. 2.Seismological Dept.IPGParisFrance

Personalised recommendations