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Science 6 October 1995:
Vol. 270. no. 5233, pp. 74 - 77
DOI: 10.1126/science.270.5233.74
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Reports

P`P` Precursors Under Africa: Evidence for Mid-Mantle Reflectors

Yves LeStunff (1),  Charles W. Wicks Jr. (2),  Barbara Romanowicz

Observations of precursors to P`P` from a recent exceptionally large deep earthquake in the Fiji Islands (moment magnitude = 7.6) at an array of broadband stations in California revealed mid-mantle reflectors near depths of 785 kilometers and 1200 kilometers under the southern African rift. Such observations, previously reported primarily in subduction zones, suggest that these reflectors may have a global character. Our analysis, which also indicated a sharp, uplifted 670-kilometer discontinuity, demonstrates the power of sparse regional broadband arrays for the study of weak, frequency-dependent features in deep-Earth structure.


Seismographic Station and Department of Geology and Geophysics, University of California at Berkeley, Berkeley, CA 94720, USA.
(1) To whom correspondence should be addressed.
(2) Present address: Institut für Geophysik, D-37075 Göttingen, Germany.


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