Topography of Earth’s inner core boundary from high-quality waveform
Precise determination of the topography of a major internal boundary of the Earth is difficult because of the trade-off with the unknown velocity structure above it. However, the discoveries of the inner core (IC) rotation and high-quality teleseismic waveform doublets make the precise mapping of th...
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| Format: | Text |
| Language: | English |
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| Online Access: | http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.210.6164 http://www.geology.illinois.edu/people/xsong/Sites/papers/song_dai08_gji.pdf |
| Summary: | Precise determination of the topography of a major internal boundary of the Earth is difficult because of the trade-off with the unknown velocity structure above it. However, the discoveries of the inner core (IC) rotation and high-quality teleseismic waveform doublets make the precise mapping of the topography of the inner core boundary (ICB) possible. Here we examine IC refracted (PKP-DF) and reflected (PKP-CD) waves recorded at the Yellowknife Array and other global stations from 14 high-quality doublets, among a large collection of doublets in S. Sandwich Islands that are recently discovered. Our results show clear evidence for spatial and temporal variations of IC reflections in traveltimes and in waveforms. If the time separation (dT) between the two members of the doublet is less than 3 yr, the IC arrivals show little temporal change in traveltimes or waveforms. If dT is greater than about 6 yr, some doublets show large variations but some others do not. The ICB regions beneath Atlantic and Indian Oceans show little temporal change. The regions that show large variations are beneath Africa and the Central America, which coincide with large seismic anomalies at the core–mantle boundary (CMB). Inside these two ICB regions, there are fine-scale (km scale) variations. The largest temporal changes of IC reflections are about 0.10 to 0.14 s, corresponding to a |
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