Seismic evidence for a detached indian lithospheric mantle beneath tibet

Science

Volumn 283, Issue 5406, 1999, Pages 1306-1309

  Kosarev, C ^a   Kind, R ^b,c   Sobolev, S V ^b   Yuan, X ^b   Hanka, W ^b   Oreshin, S ^a  

^a SCHMIDT INSTITUTE OF PHYSICS OF THE EARTH   (Russian Federation)

^b GFZ GERMAN RESEARCH CENTRE FOR GEOSCIENCES   (Germany)

^c FREIE UNIVERSITÄT BERLIN   (Germany)

Author keywords

[No Author keywords available]

Indexed keywords

LITHOSPHERIC STRUCTURE; SEISMIC WAVE;

ARTICLE; ASIA; EARTHQUAKE; GEOGRAPHY; GEOLOGY; INDIA; NATURAL SCIENCE; PRIORITY JOURNAL;

CHINA;

MOHO;

EID: 0039255338     PISSN: 00368075     EISSN: None     Source Type: Journal    
DOI: 10.1126/science.283.5406.1306     Document Type: Article

References (41)

1. P. Molnar, Philos. Trans. R. Soc. London Ser. A 326, 33 (1988).
2. T. J. Owens and C. Zandt, Nature 387, 37 (1997).
3. L. Zhu, T. J. Owens, G. E. Randall, Bull. Seismol. Soc. Am. 85, 1531 (1995).
4. P. Molnar, P. England, J. Martinod, Rev. Geophys. 31, 357 (1993).
5. D. E. McNamara, W. R. Walter, T. J. Owens, C. J. Ammon, J. Geophys. Res. 102, 493 (1997).
6. D. Willett and C. Beaumont, Nature 369, 642 (1994).
7. D. E. McNamara, T. J. Owens, P. G. Silver, F. T. Wu, J. Geophys. Res. 99, 13655 (1994).
8. D. E. McNamara, T. J. Owens, W. R. Walter, ibid. 100, 22215 (1995).
9. J. Ni and M. Barazangi, Geophys. J. R. Astron. Soc. 72, 665 (1983).
10. Y. Jin, M. McNutt, Y. Zhu, J. Geophys. Res. 101, 11275 (1996).
11. W. Zhao et al., Nature 366, 557 (1993).
12. K. D. Nelson et al., Science 274, 1684 (1996).
13. R. Kind et al., ibid., p. 1692.
14. L. D. Brown et al., ibid., p. 1688.
15. A. Hirn et al., Nature 307, 25 (1984); A. Hirn et al., ibid. 375, 571 (1995).
16. A. Hirn et al., Nature 307, 25 (1984); A. Hirn et al., ibid. 375, 571 (1995).
17. G. Wittlinger et al., Earth Planet. Sci. Lett. 139, 363 (1996).
18. S. Turner et al., Nature 364, 50 (1993).
19. P. Molnar and W. P. Chen, J. Geophys. Res. 88, 1180 (1983).
20. T. J. Owens, G. E. Randall, F. T. Wu, R. Zeng, Bull. Seismol. Soc. Am. 83, 1959 (1993).
21. R. Zeng, Z. Ding, Q. Wu, Pure Appl. Geophys. 145, 425 (1995).
22. L Zhao, M. K. Sen, P. Stoffa, C. Frohlich, Geophys. J. Int. 125, 355 (1996).
23. X. Yuan, J. Ni, R. Kind, J. Mechie, E. Sandvol, J. Geophys. Res. 102, 27491 (1997).
24. T. J. Owens, G. Zandt, S. R. Taylor, ibid. 89, 7783 (1984).
25. M. G. Bostock, Nature 390, 392 (1997).
26. C. H. Jones and R. A. Phinney, J. Geophys. Res. 103, 10065 (1998).
27. B. L. N. Kennett and E. R. Engdahl, Geophys. J. Int. 105, 429 (1991).
28. Crustal multiples, which means a P-to-S conversion plus two additional P legs or one P and one S leg in the crust, are frequently observed and used in inversions of crustal structure [R. Kind, G. L. Kosarev, N. V. Petersen, Geophys. J. Int. 121, 191 (1995)]. They interfere with original conversions from the depth range between 200 and 300 km. Multiples may be identified by their difference in slowness compared with the original conversions; however, this is sometimes difficult to observe. The migration reduces the influence of multiples if sufficient ray coverage is available. The separation of crustal multiples from inclined structures in the mantle is relatively easy if the Moho is not, or only weakly, inclined (as in Tibet) and structures in the mantle are strongly inclined. The ZCB has a north dip of 20°, whereas the Moho above dips south by 2° to 3°, ruling out the possibility of the ZCB being a crustal multiple. The NCZ dips south by ∼25°, whereas PP and PS crustal multiples would have dips of 8° to 9°. This also rules out the possibility that the NCZ could be a Moho multiple.
29. R. Kind, J Geophys. 58, 146 (1985).
30. S. V. Sobolev et al., Earth Planet. Sci. Lett. 139, 147 (1996).
31. Other factors such as remnants of the lower crust subducted along with the Indian lithospheric mantle or a lattice-preferred orientation of olivine crystals in the interplate shear zone may also contribute to the observed velocity contrast at the ZCB. However, this is difficult to quantify until more data about the conversion coefficient and thickness of the ZCB is available.
32. Although north of 30.5° latitude we have data only from the relatively few stations of the PASSCAL experiment, there is practically no difference between the signal-to-noise ratio of the averaged converted phases and that of the more numerous data from the INDEPTH II/GEDEPTH experiment in the south. The averaged amplitudes over the entire profile are at the Moho ≥ 10% of the incident P wave; at the bright spot 6 to 8%; and at the ZCB, NCZ, 410-, and 660-km discontinuities 4 to 6%. The overall noise level is about 2 to 4%.
33. 3), a cratonic lithospheric mantle is still much more buoyant in the asthenosphere than a young lithospheric mantle.
34. 3), a cratonic lithospheric mantle is still much more buoyant in the asthenosphere than a young lithospheric mantle.
35. 3), a cratonic lithospheric mantle is still much more buoyant in the asthenosphere than a young lithospheric mantle.
36. 3), a cratonic lithospheric mantle is still much more buoyant in the asthenosphere than a young lithospheric mantle.
37. 3), a cratonic lithospheric mantle is still much more buoyant in the asthenosphere than a young lithospheric mantle.
38. 3), a cratonic lithospheric mantle is still much more buoyant in the asthenosphere than a young lithospheric mantle.
39. T. H. Jordan, Nature 274, 544 (1978).
40. The travel time curves of the P phase and the P-to-S converted phases have different slopes. To make these travel time curves parallel, we compressed the time scale at distances smaller than 67° epicentral distance and expanded it at larger distances. The time scale is therefore only valid for 67° epicentral distance (22, 24). Such a move out correction is common procedure in steep-angle reflection experiments.
41. Supported by the German Bundesministerium für Bildung und Forschung. The INDEPTH II/GEDEPTH experiment was supported by the GeoForschungsZentrum Potsdam, the Deutsche Forschungsgemeinschaft, the U.S. National Science Foundation, and the Chinese Academy of Geological Sciences. Data from the Tibet PASSCAL experiment were collected in a joint project between the University of South California (T. Owens and G. Randall), State University of New York-Binghamton (F. Wu), and the research group of R. Zeng, Institute of Geophysics, State Seismological Bureau, China. We thank X. Li for computational support, and C. Estabrook, G. Bock, and D. Harlov for carefully reading the manuscript.