Explosion seismic reflections from the Earth’s core |
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Authors: | H Thybo AR Ross |
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Institution: | a Geological Institute, University of Copenhagen, Øster Voldgade 10, 1350 Copenhagen K, Denmark b Center for Regional Geophysical and Geoecological Studies (GEON), Chistyi per. 4, Moscow 119034, Russia |
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Abstract: | Recent seismological studies have presented evidence for the existence of a layer with ultra-low seismic velocities at the core-mantle boundary at ca. 2900 km depth. We report high-amplitude, high-frequency, and laterally coherent seismic arrivals from three nuclear explosions in Siberia. With recording station intervals of 15 km, the seismic phases are readily correlated and show the presence of a thin, ultra-low velocity zone in a region where it was not previously reported. The duration and complexity of the arrivals are inconsistent with a simple core-mantle boundary and require a hitherto unidentified, kilometre-scale, fine structure in the ultra-low velocity zone. The observations may be explained by a ca. 7 km thick, two-layer, ultra-low velocity zone with exceptional low velocities, which indicate the presence of high percentages of melt (>15%), in particular in the lower part of the zone. Waveform variation implies lateral change in the thickness and physical properties of the ultra-low velocity zone with a wavelength of less than 100 km. |
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Keywords: | core-mantle boundary ultra-low velocity zone lower mantle nuclear explosions reflection seismology long-range explosion seismology |
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