The nature of the 660-kilometer upper-mantle seismic discontinuity from precursors to the PP phase

Science

Volumn 274, Issue 5290, 1996, Pages 1179-1182

  Estabrook, Charles H ^a   Kind, Rainer ^a,b  

^a GFZ GERMAN RESEARCH CENTRE FOR GEOSCIENCES   (Germany)

^b FREIE UNIVERSITÄT BERLIN   (Germany)

Author keywords

[No Author keywords available]

Indexed keywords

ARTICLE; ASTRONOMY; GEOLOGY; PRIORITY JOURNAL; SHEAR STRESS;

DISCONTINUITY 660 KM; MANTLE (UPPER); PP PHASE;

EID: 0029659877     PISSN: 00368075     EISSN: None     Source Type: Journal    
DOI: 10.1126/science.274.5290.1179     Document Type: Article

References (46)

1. L. P. Vinnik, Phys. Earth Planet. Inter. 15, 39 (1977): K. Stammler et al., Geophys. Res. Lett. 19, 1563 (1992).
2. L. P. Vinnik, Phys. Earth Planet. Inter. 15, 39 (1977): K. Stammler et al., Geophys. Res. Lett. 19, 1563 (1992).
3. C. W. Wicks and M. A. Richards, Geophys. J. Int. 107, 279 (1991); G. Bock and R. Kind, ibid., p. 117.
4. C. W. Wicks and M. A. Richards, Geophys. J. Int. 107, 279 (1991); G. Bock and R. Kind, ibid., p. 117.
5. P. M. Shearer, J. Geophys. Res. 96, 18147 (1991).
6. J. Gossler and R. Kind, Earth Planet. Sci. Lett. 138, 1 (1996).
7. P. M. Shearer, Geophys. J. Int. 115, 878 (1993).
8. N. Wajeman, Geophys. Res. Lett. 15, 669 (1988).
9. E. Ito and E. Takahashi, J. Geophys. Res. 94, 10637 (1989).
10. T. Duffy and D. L. Anderson, ibid., p. 1895.
11. T. Irifune, Phys. Earth Planet. Inter. 45, 324 (1987).
12. PP is a P wave that reflects once from Earth's surface. P'P' (PKPPKP) is like PP but travels through the core. PzP are underside reflections, where z is the depth of the reflection (for example, P660P is a P wave reflected from a depth of 660 km). Pdzd are topside reflections where d is either p or s (for example, Ps660p is a P wave with a source- or receiverside S-P reflection-conversion).
13. H. M. Benz and J. E. Vidale, Nature 365, 147 (1993).
14. N. Petersen et al., Geophys. Res. Lett. 20, 859 (1993); M. G. Bostock, ibid. 23, 1593 (1996).
15. N. Petersen et al., Geophys. Res. Lett. 20, 859 (1993); M. G. Bostock, ibid. 23, 1593 (1996).
16. L. Vinnik, G. Kosarev. N. Petersen, ibid., p. 1485.
17. A. C. Lees, M. S. T. Bukowinski, R. Jeanloz, J. Geophys. Res. 88, 8145 (1983).
18. U. R. Christensen and D. A. Yuen, ibid. 89, 4389 (1984).
19. R. van der Hilst, E. R. Engdahl, W. Spakman, Geophys. J. Int. 115, 264 (1993).
20. U. Christensen, Earth Planet. Sci. Lett. 140, 27 (1996); H.-P. Bunge, M. A. Richards, J. R. Baumgardner, Nature 379, 436 (1996); P. J. Tackley, D. J. Stevenson, G. A. Glatzmaier, G. Schubert, J Geophys. Res. 99, 15877 (1994).
21. U. Christensen, Earth Planet. Sci. Lett. 140, 27 (1996); H.-P. Bunge, M. A. Richards, J. R. Baumgardner, Nature 379, 436 (1996); P. J. Tackley, D. J. Stevenson, G. A. Glatzmaier, G. Schubert, J Geophys. Res. 99, 15877 (1994).
22. U. Christensen, Earth Planet. Sci. Lett. 140, 27 (1996); H.-P. Bunge, M. A. Richards, J. R. Baumgardner, Nature 379, 436 (1996); P. J. Tackley, D. J. Stevenson, G. A. Glatzmaier, G. Schubert, J Geophys. Res. 99, 15877 (1994).
23. The data were provided by IRIS-Seattle (Incorporated Research Institutions for Seismology) as FARM (fast archive recovery method) data volumes.
24. We calculated the SNR from the peak-to-peak ampiitude (PTPA) 65 to 5 s before the predicted PP arrival time versus the PTPA from the PP time to 60 s after, using the band-pass-filtered seismograms (10 to 50 s).
25. K. Stammler, Comput. Geosci. 19, 135 (1993). The data were detrended and filtered with a causal three-pole bandpass filter between 3 and 50 s before deconvolution and filtered again with a threepole acausal bandpass filter between 10 and 50 s to shift the weighting toward longer periods. The acausal gilter produced symmetric side lobes, which appeared in the synthetics (Fig. 1B, appearing ∼60 s before P and PKP) but not in the data. The stacking procedure apparently canceled out this effect when applied to the data because of the sheer number of events. The PP phase was deconvolved from the entire seismogram to account for varying source-time histories and radiation patterns. To enhance the amplitude of the precursors to PP. we aligned the seismograms on the resulting spike and slant-stacked (stacking along a traveltime curve) to obtain the slownesses (inverse of apparent velocity) of the PP phase and its precursors (1).
26. 1 is from the Preliminary Reference Earth Model [A. M. Dziewonski and D. L. Anderson, Phys. Earth Planet. Inter. 25, 297 (1981)]. Density is from AK135 [B. L. N. Kennett, E. R. Engdahl, R. Buland, Geophys. J. Int. 122, 108 (1995)].
27. 1 is from the Preliminary Reference Earth Model [A. M. Dziewonski and D. L. Anderson, Phys. Earth Planet. Inter. 25, 297 (1981)]. Density is from AK135 [B. L. N. Kennett, E. R. Engdahl, R. Buland, Geophys. J. Int. 122, 108 (1995)].
28. 1 is from the Preliminary Reference Earth Model [A. M. Dziewonski and D. L. Anderson, Phys. Earth Planet. Inter. 25, 297 (1981)]. Density is from AK135 [B. L. N. Kennett, E. R. Engdahl, R. Buland, Geophys. J. Int. 122, 108 (1995)].
29. F. Neele, H. de Regt, J. VanDecar, in preparation.
30. p = √(λ + 2μ)/ρ = √(κ + 4μ/3)/ρ, where λ and μ are the Lamé parameters (μ is also known as the shear modulus) and κis the bulk modulus: Φ = (λ + 2μ/3)/ρ = κ/ρ
31. K. Aki and P. Richards, Quantitative Seismology: Theory and Methods (Freeman, San Francisco, 1980), vol. 1.
32. J. C. Jaeger, Elasticity, Fracture, and Flow: With Engineering and Geological Applications (Chapman and Hall, London, 1969).
33. s and ρ.
34. J. Ita and L. Stixrude, J. Geophys. Res. 97, 6849 (1992).
35. K. E. Bullen and B. A. Bolt, An Introduction to the Theory of Seismology (Cambridge Univ. Press, Cambridge, 1987).
36. R. Kind, J. Geophys. 42, 191 (1976).
37. S. P. Grand and D. V. Helmberger, Geophys. J. R. Astron. Soc. 76, 399 (1984); M. C. Walck, ibid., p. 697; L. E. Jones, J, Mori, D. V. Helmberger, J. Geophys. Res. 97, 8765 (1992).
38. S. P. Grand and D. V. Helmberger, Geophys. J. R. Astron. Soc. 76, 399 (1984); M. C. Walck, ibid., p. 697; L. E. Jones, J, Mori, D. V. Helmberger, J. Geophys. Res. 97, 8765 (1992).
39. S. P. Grand and D. V. Helmberger, Geophys. J. R. Astron. Soc. 76, 399 (1984); M. C. Walck, ibid., p. 697; L. E. Jones, J, Mori, D. V. Helmberger, J. Geophys. Res. 97, 8765 (1992).
40. J. R. Bowman and B. L. N. Kennett, Geophys. J. Int. 101, 411 (1990).
41. T. Ryberg et al., Ann. Geophys. (abstract) (1996), p. C68.
42. P. Vacher. A. Mocquet, C. Sotin, ibid., p. C41.
43. B. H. Hager and M. A. Richards, Philos. Trans. R. Soc. London Ser. A 328. 309 (1989); A. M. Forte, A. M. Dziewonski, R. J. O'Connell, Science 268, 386 (1995).
44. B. H. Hager and M. A. Richards, Philos. Trans. R. Soc. London Ser. A 328. 309 (1989); A. M. Forte, A. M. Dziewonski, R. J. O'Connell, Science 268, 386 (1995).
45. R. Kind, J. Geophys. 45, 373 (1979).
46. We thank G. Bock, J. Gossler, W. Hanka, F. Krüger, P. Richards, T. Ryberg, C. Scholz, and S. Sobolev for helpful discussions and reviews. We thank IRIS-Seattle for the FARM tapes and contributing stations from the Federation of Digital Seismic Networks. K. Stammler, R. Benson, and T. McSweeny supplied software. Supported by the Deutsche Forschungsgemeinschaft.