Seismic imaging of upper-mantle structure with new evidence for a 520-km discontinuity

Stacked images of long-period seismic data reveal many phases, some not previously observed, which are caused by reflections and conversions at discontinuities in the Earth's upper mantle. These images support the existence of discontinuities at 410, 520 and 660km depth, but no evidence is found for a significant interface at 220 km.

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