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Localized boundary layer below the mid-Pacific velocity anomaly identified from a PeP precursor

Mori, Jim and Helmberger, Donald V. (1995) Localized boundary layer below the mid-Pacific velocity anomaly identified from a PeP precursor. Journal of Geophysical Research B, 100 (B10). 20,359-20,365. ISSN 0148-0227. doi:10.1029/95JB02243.

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Dense record sections from deep earthquakes in Fiji and Argentina recorded on hundreds of short-period stations in California at distances of 81° to 85° are used to investigate the detailed P wave velocity structure above the core-mantle boundary (CMB). In the Fiji data a secondary phase arriving 2 to 4 s after the direct P is identified as a precursor to PcP. This phase provides good evidence for a reflection off the top of a thin low-velocity layer above the CMB. Comparisons to synthetic seismograms indicate a layer thickness of 10 km and a velocity reduction of 5%–10% compared to the overlying mantle. A record section from an Argentina event does not show the PcP precursor, indicating that the low-velocity layer is not a global feature. This thin low-velocity layer is in the same place as a much larger S wave velocity anomaly in the lower mantle and is probably indicative of a boundary layer just above the CMB under the mid-Pacific.

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Additional Information:© 1995 American Geophysical Union. Received May 8, 1995; revised July 18, 1995; accepted July 25, 1995. Helpful comments on this paper were provided by J. Vidale, G. Choy, T. Lay, J. Revenaugh, and M. Wysession. Xiangming Ding helped with Figure 1. This research was supported in part by NSF grant EAR9316441. Contribution 5564, Division of Geological and Planetary Sciences, California Institute of Technology.
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Caltech Division of Geological and Planetary Sciences5564
Issue or Number:B10
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Official Citation: Mori, J. and D. V. Helmberger (1995), Localized boundary layer below the mid-Pacific velocity anomaly identified from a PcP precursor, J. Geophys. Res., 100(B10), 20,359–20,365, doi:10.1029/95JB02243.
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:35703
Deposited By: Ruth Sustaita
Deposited On:28 Nov 2012 18:18
Last Modified:09 Nov 2021 23:17

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