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

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Science  06 Oct 1995:
Vol. 270, Issue 5233, pp. 74-77
DOI: 10.1126/science.270.5233.74


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.

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