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Published February 1984 | Published
Journal Article Open

Anisotropy and shear-velocity heterogeneities in the upper mantle


Long-period surface waves are used to map lateral heterogeneities of velocity and anisotropy in the upper mantle. The dispersion curves are expanded in spherical harmonics up to degree 6 and inverted to find the depth structure. The data are corrected for the effect of surface layers and both Love and Rayleigh waves are used. Shear wave velocity and shear polarization anisotropy can be resolved down to a depth of about 450 km. The shear wave velocity distribution to 200 km depth correlates with surface tectonics, except in a few anomalous regions. Below that depth the correlation vanishes. Cold subducted material shows up weakly at 350 km as fast S-wave anomalies. In the transition region a large scale pattern appears with fast mantle in the South-Atlantic. S-anisotropy at 200 km can resolve uprising or downwelling currents under some ridges and subduction zones. The Pacific shows a NW-SE fabric.

Additional Information

© 1984 American Geophysical Union. Received October 24, 1983; accepted January 10, 1984. Paper number 4L0118. The authors wish to thank N. Jobert, H. Kanamori, J-P. Montagner, B. Hager, and A. Tarantola for helpful discussions. J. Woodhouse and A. Dziewonski made available to us a preprint of their work prior to publication, and a computer program. This research was supported by NASA grant NSG-7610 and NSF grant EAR811-5236. Contribution no. 3989, Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California 91125.

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