A scattering region near the core-mantle boundary under the North Atlantic
We analysed PcP precursors in seven events from Central America, recorded at the UK array of short-period stations, to determine the most likely source of this signal. Combinations of observations of slowness, traveltime and backazimuth were used to investigate the properties of the phase, with the...
| Published in: | Geophysical Journal International |
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| Main Authors: | , |
| Format: | Text |
| Language: | English |
| Published: |
Oxford University Press
2004
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| Subjects: | |
| Online Access: | http://gji.oxfordjournals.org/cgi/content/short/158/2/625 https://doi.org/10.1111/j.1365-246X.2004.02306.x |
| Summary: | We analysed PcP precursors in seven events from Central America, recorded at the UK array of short-period stations, to determine the most likely source of this signal. Combinations of observations of slowness, traveltime and backazimuth were used to investigate the properties of the phase, with the result that its source is identified as P to P scattering from an anomalous region in the lower mantle, within D?. Using a joint likelihood method, the best estimate of a point source for scattering is at 44.0°N, 71.5°W (under Nova Scotia) and 2720 km depth. Analysis of the spectrum of the scattered signal indicates that the region contains small-scale heterogeneities on the order of 0.6 to 0.7 km, and is ~700 km in size. The velocity contrast between the scattering bodies and ambient mantle is as high as +0.4 to +0.7 per cent Vp and +1.4 to +6.6 per cent Vs . On account of their small size, positive velocity anomaly and association with the reconstructed position of ancient subducted material, we conclude that they represent chemical heterogeneity in the lower mantle. |
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