Quick Search:    advanced search

GSW Home   GeoRef Home   My GSW Alerts   Contact GSW   About GSW   Journals List   Help

This Article Full Text (PDF) References Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by FAIRBORN, J. W. Search for Related Content GeoRef GeoRef Citation

Shear wave velocities in the lower mantle

DEPARTMENT OF GEOLOGY AND GEOPHYSICS MASSACHUSETTS INSTITUTE OF TECHNOLOGY, CAMBRIDGE, MASSACHUSETTS

Abstract

The Large Aperture Seismic Array in eastern Montana was used to measure the travel times and dT/d of earthquake-generated shear waves for the purpose of determining lower-mantle shear velocities. The data were limited to epicentral distances between 27 and 95 degrees. To convert uncertainties in the dT/d measurements to uncertainties in the computed velocities, the data were inverted by a Monte Carlo procedure. The computer randomly generated velocity models, and those which satisfied prescribed travel time and dT/d-versus- limits were considered as possible models for the real earth. The dT/d curve possessed anomalously steep slopes between 27-30 and 65-75 degrees, and the corresponding velocity models had increased gradients between the approximate depths of 700-800 and 1550-2100 kilometers. The slope of the dT/d curve also decreased at about 88 degrees which may indicate a decrease in velocity gradient several hundred kilometers above the core-mantle boundary. For epicentral distances greater than 27 degrees the observed travel times to LASA were greater than the expected J-B times. Although vague, a systematic increase in the observed residuals appeared to exist between 40 and 60 degrees which agreed with the J-B residuals of the computed models.

Footnotes

^* Now at Chevron Oil Field Research Company, La Habra, California.

This article has been cited by other articles:

				K. L. KAILA, V. G. KRISHNA, and H. NARAIN Upper mantle shear-wave velocity structure in the Japan region Bulletin of the Seismological Society of America, April 1, 1974; 64(2): 355 - 374. [Abstract] [PDF]

				M. NIAZI SH travel times and lateral heterogeneities in the lower mantle Bulletin of the Seismological Society of America, December 1, 1973; 63(6-1): 2035 - 2046. [Abstract] [PDF]

				A. L. HALES and J. L. ROBERTS Shear velocities in the lower mantle and the radius of the core Bulletin of the Seismological Society of America, October 1, 1970; 60(5): 1427 - 1436. [Abstract] [PDF]