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A study of lateral inhomogeneities in the upper mantle by multiple Scs travel-time residuals

Okal, Emile A. and Anderson, Don L. (1975) A study of lateral inhomogeneities in the upper mantle by multiple Scs travel-time residuals. Geophysical Research Letters, 2 (8). pp. 313-316. ISSN 0094-8276. doi:10.1029/GL002i008p00313.

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An analysis of records of multiply reflected ScS phases from ten deep‐focus earthquakes yields near‐vertical one‐way travel‐time residuals varying from +5.0 to −3.5 s. Continental and oceanic residuals overlap and both indicate large lateral variations. Similar values are found for the older oceanic basins and for continental shields. Most, if not all, of the variations can be attributed to differences in the lithosphere and asthenosphere. The mantle under Hawaii, Iceland and Trindade (South Atlantic) Islands is anomalously slow, all being postulated hotspots. In the case of Trindade, petrological data is consistent with a pronounced low‐velocity zone and large S delays. Some recent studies assumed that stations on oceanic islands were representative of the ocean as a whole and it has been suggested that continent‐ocean differences extend deeper than 400 km. The present results indicate that oceanic islands are anomalous, and that differences between oceans and continents need not extend below 200 km. This does not rule out the existence of deep lateral inhomogeneities, but only the proposal that continents, in general, are faster than oceans to depths greater than 400 km.

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Additional Information:© 1974 by the American Geophysical Union. Received July 2, 1975; accepted July 16, 1975. This research was supported by the Advanced Research Project Agency of the Department of Defence and was monitored by the Air Force Office of Scientific Research under contract F44620-72-C-0078. Contribution 2641, Division of Geological and Planetary Sciences, California Institute of Technology.
Group:Seismological Laboratory
Funding AgencyGrant Number
Advanced Research Projects Agency (ARPA)UNSPECIFIED
Air Force Office of Scientific Research (AFOSR)F44620-72-C-0078
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Caltech Division of Geological and Planetary Sciences2641
Issue or Number:8
Record Number:CaltechAUTHORS:20181127-123929350
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Official Citation:Okal, E. A. and Anderson, D. L. (1975), A study of lateral inhomogeneities in the upper mantle by multiple Scs travel‐time residuals. Geophys. Res. Lett., 2: 313-316. doi:10.1029/GL002i008p00313
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:91226
Deposited By: Tony Diaz
Deposited On:27 Nov 2018 21:54
Last Modified:16 Nov 2021 03:39

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