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SH travel times and lateral heterogeneities in the lower mantle

Niazi, Mansour (1973) SH travel times and lateral heterogeneities in the lower mantle. Bulletin of the Seismological Society of America, 63 (6). pp. 2035-2046. ISSN 0037-1106.

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The horizontal long-period seismograms of two shallow earthquakes in Turkey and Iran recorded in selected azimuths are combined for travel-time studies of the SH wave beyond the angular distance of 40°. The observed travel times along two profiles which sample the deep mantle in the vicinity of Iceland and the North Pole show monotonically increasing differences beyond 65°, indicating lateral heterogeneity in the lower mantle. The travel-time difference becomes as large as 7 sec at 95°, implying a variation as much as 0.06 km/sec, or about 1 per cent, in the shear-wave velocity near 2,500 km depth. Inversion of observations, adjusted to surface foci, results in an average lower mantle structure with lower shear velocities than those given by Jeffreys. The difference exceeds 0.1 km/sec at the core boundary. The arrival time and signature of S waves recorded in Greenland show anomalous features which may be related to deep seated anomalous zones associated with the Mid-Atlantic Ridge system.

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Additional Information:© 1973 Seismological Society of America. Manuscript received May 7, 1973. Professors Don L. Anderson and Donald V. Helmberger kindly read the manuscript and made valuable suggestions. Some of the computer programs used in this study were originally written by Drs. H. Kanamori, J. Whitcomb, and B. Julian. Graphs were prepared by Mr. Laszlo Lenches. This research was supported by the Advanced Research Projects Agency of the Department of Defense and was monitored by the Air Force Office of Scientific Research under Contract F44620-72-C-0078.
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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 Sciences2347
Issue or Number:6
Record Number:CaltechAUTHORS:20140915-092859112
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:49691
Deposited By: Tony Diaz
Deposited On:15 Sep 2014 17:30
Last Modified:03 Oct 2019 07:16

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