1. 1. Gutenberg, B. & Richter, C. F. On seismic waves: I. Gerlands Beitr. z. Geophysik. 43, 56-133 (1934). 2. Bullen, K. E. & Burke-Gaffney, T. N. Diffracted seismic waves near the PKP caustic. Geophys. J. Int. 1, 9-17 (1958). 3. Gutenberg, B. The boundary of the Earth's inner core. Eos 38, 750-753 (1957). 4. Bolt, B. A. Gutenberg's early PKP observations. Nature 196, 122-124 (1962). 5. Sacks, I. S. & Saa, G. The structure of the transition zone between the inner core and the outer core. Yb. Carnegie Inst. Wash. 69, 419-426 (1969). 6. Haddon, R. A. W. Corrugations on the CMB or transition layers between inner and outer cores? Eos 53,600(1972). 7. Cleary, J. R. & Haddon, R. A. W. Seismic wave scattering near the core-man tie boundary: a new interpretation of precursors to PKP. Nature 240, 549-551 (1972). 8. Doornbos, D. J. & Husebye, E. S. Array analysis of PKP phases and their precursors. Phys. Earth Planet. Inter. 5, 387-399 (1972). 9. King, D. W., Haddon, R. A. W. & Cleary, J. R. Array analysis of precursors to PKIKP, in the distance range 129° to 142°. Geophys. J. R. Astron. Soc. 37, 157-173 (1974). 10. Husebye, E. S., King, D. W. & Haddon, R. A. W. Precursors to PKIKPand seismic wave scattering near the mantle-core boundary. /. Geophys. Res. 81, 1870-1882 (1976). 11. Doornbos, D. J. Characteristics of lower mantle inhomogeneities from scattered waves. Geophys. J. R. . Astron. Soc. 49, 541-542 (1976). 12. Doornbos, D. J. & Vlaar, N. J. Regions of seismic wave scattering in the Earth's mantle and precursors to PKP. Nature 243, 58-61 (1973). 13. Haddon, R. A. W. & Cleary, J. R. Evidence for scattering of seismic PKP waves near the mantle-core boundary. Phys. Earth Planet. Inter. 8, 211-234 (1974). 14. Doornbos, D. J. On seismic-wave scattering by a rough core-mantle boundary. Geophys. J. R. Astron. Soc. 53, 643-662(1978). 15. Bataille, K. & Flatte, S. M. Inhomogeneities near the core-mantle boundary inferred from short-period scattered PKP waves recorded at the global digital seismograph network. /. Geophys. Res. 93, 15057-15064 (1988). 16. Bataille, K., Wu, R. S. & Flatte, S. M. Inhomogeneities near the core-mantle boundary evidenced from scattered waves: a review. Pure Appl. Geophys. 132, 151-173 (1990). 17. Davies, G. F. Geophysical and isotopic constraints on mantle convection: an interim synthesis /. Geophys. Res. 89, 6017-6040 (1984). 18. Davies, G. F. Mantle plumes, mantle stirring and hotspot chemistry. Earth Planet. Sci. Lett. 99,94-109 (1990). 19. Gurnis, M. & Davies, G. F. Mixing in numerical models of mantle convection incorporating plate tectonics. /. Geophys. Res. 91, 6375-6395 (1986). 20. Efron, B. & Tibshirani, R. Statistical data analysis in the computer age. Science 253, 390-395 (1991). 21. Chernov, L. A. Wave Propagation in a Random Medium (trans. Silverman, R. A.) (McGraw-Hill, New York, 1960). 22. Wu, R. S. & Aki, K. Elastic wave scattering by a random medium and the small-scale inhomogeneities in the lithosphere. /. Geophys. Res. 90, 10261-10273 (1985). 23. Cormier, V. Time domain modeling of PKIKP precursors for constraints on the heterogeneity in the lowermost mantle. Geophys. J. Int. 212, 725-736 (1995). 24. Bhattacharyya, J., Shearer, P. M. & Masters, G. Inner core attenuation from short-period PKP(BC) versus PKP(DF) waveforms. Geophys. J. Int. 114, 1-11 (1993). 25. Menke, W. Few 5-20 km corrugations on the core-mantle boundary. Geophys. Res. Lett. 13, 1501-1504(1986). 26. Vidale, J. E. & Benz, H. M. A sharp and flat section of the core-mantle boundary. Nature 359,627-629 (1992). 27. Chang, A. C. & Cleary, J. R. Precursors to PKKP Bull. Seismol. Soc. Am. 68, 1059-1079 (1978). 28. Chang, A. C. & Cleary, J. R. Scattered PKKP: further evidence for scattering at a rough core-mantle boundary. Phys. Earth Planet. Inter. 24, 15-29 (1981). 29. Doornbos, D. J. The effect of a rough core-mantle boundary on PKKP. Phys. Earth Planet. Inter. 21, 351-358 (1980). 30. Woodward, R. L. & Masters, T. G. Lower-mantle structure from ScS-S differential travel times. Nature 352,231-233(1991). 31. Su, W.-J. & Dziewonski, A. M. Predominance of long-wavelength heterogeneity in the mantle. Nature 352,121-126(1991). 32. Masters, T. G., Johnson, S., Laske, G. & Bolton, H. A shear-velocity model of the mantle. Phil Trans. R. Soc. Lond. A 354, 1-27 (1996). 33. Lay, T. Structure of the core-mantle transition zone: a chemical and thermal boundary layer. £05 70, 49, 54-55, 58-59 (1989). 34. Loper, D. E. & Lay, T. The core-mantle boundary region. /. Geophys. Res. 100, 6397-6420 (1995). 35. Passier, M. L. & Sneider, R. K. On the presence of intermediate-scale heterogeneity in the mantle. Geophys. J. Int. 123, 817-837 (1995). 36. Christensen, U. R. & Hofmann, A. W. Segregation of subducted oceanic crust in the convecting mantle./. Geophys. Res. 99, 19867-19884 (1994). 37. Hedlin, M. A. H., Shearer, P. M. & Earle, P. Imaging CMB scatterers through migration of GSN PKPdf precursor recordings. Eos 76, F402 (1995). 38. Dziewonski, A. & Anderson, D. L. Preliminary reference earth model. Phys. Earth Planet. Inter. 25, 297-356 (1981). 39. Kennett, B. L. N. (ed.) IASPEI 1991 Seismological Tables (Res. Sch. Earth Sci., Aust. Nat. Univ., Canberra, 1991). 40. Morelli, A. & Dziewonski, A. M. Body wave traveltimes and a spherically symmetric P- and S-wave velocity model. Geophys. J. Int. 112, 178-194 (1993).