Letter | Published:

Seismic Wave Scattering Near Caustics: Observations of PKKP Precursors

Naturevolume 247pages352353 (1974) | Download Citation



ANALYSIS of precursors to PKP1,2 has provided evidence for the existence of scattering structures in the deep mantle. It has been argued that the observability of the scattered waves is closely related to the presence of a caustic because of the focusing effect and because the scattered waves can enter the shadow zone at the concave side of the caustic, where they may manifest themselves as first arrivals. If that interpretation is correct, then in suitable circumstances the scattering phenomenon should also be identifiable near other caustics. The Earth's core forms a caustic not only for PKP phases, but also for SKP, PKKP, SKKP etc. and thus there is, in principle, the opportunity to test the interpretation. In practice there are a number of limitations: first, the latter phases themselves are one or more orders of magnitude smaller than PKP; second, at the time of arrival of these phases the seismic traces are, in general, still ‘noisy’. This practically excludes identification from single traces. We have used data from the Norwegian Seismic Array (NORSAR) and here observations in the shadow of the PKKP caustic will be reported. The PKKP caustic agrees mostly with the one of PKP; both caustics extend throughout the whole mantle, in contrast to those of, for example, SKP and SKKP.

Access optionsAccess options

Rent or Buy article

Get time limited or full article access on ReadCube.


All prices are NET prices.


  1. 1

    Cleary, J. R., and Haddon, R. A. W., Nature, 240, 549 (1972).

  2. 2

    Doornbos, D. J., and Vlaar, N. J., Nature phys. Sci., 243, 58 (1973).

  3. 3

    Davies, D., Kelly, E. J., and Filson, J. R., Nature phys. Sci., 232, 8 (1971).

  4. 4

    Doornbos, D. J., and Husebye, E. S., Phys. Earth Planet. Int., 5, 387 (1972).

  5. 5

    Buchbinder, G. R., Bull. seism. Soc. Am., 61, 429 (1971).

  6. 6

    Engdahl, E. R., thesis, Saint Louis University (1968).

  7. 7

    Davies, D., and Sheppard, R. M., Nature, 239, 318 (1972).

  8. 8

    Julian, B. R., and Sengupta, M. K., Nature, 242, 443 (1973).

  9. 9

    Needham, R. E., and Davies, D., Nature, 244, 152 (1973).

Download references

Author information


  1. Vening Meinesz Laboratory, University of Utrecht, Lucas Bolwerk 7, Utrecht, The Netherlands

    • D. J. DOORNBOS


  1. Search for D. J. DOORNBOS in:

About this article

Publication history


Issue Date



Further reading


By submitting a comment you agree to abide by our Terms and Community Guidelines. If you find something abusive or that does not comply with our terms or guidelines please flag it as inappropriate.