| Summary: | A new technique utilizing theoretical wave forms has been developed to determine precise shear wave travel times. This technique was applied to long-period World-Wide Standard Seismograph Network and Canadian network seismograms of five large nuclear explosions to obtain a surface focus shear wave data set containing about 100 travel times for distances greater than 30°. Very little scatter is present in the data from Novaya Zemlya and the Nevada test site, and so a reliable inversion to a lower mantle velocity structure is permitted. This velocity model, based on the 59 travel times from Novaya Zemlya, has significantly more structure than earlier models. The model, Sl, has proved to be appropriate for free oscillations as well as for travel times. This model should be useful in studying both lateral inhomogeneities and the mineralogical composition of the earth's mantle. © 1975 American Geophysical Union. Received February 14, 1975; revised July 28, 1975; accepted July 31, 1975. I would like to thank Don L. Anderson for his many helpful comments and suggestions throughout this study and for critically reading this manuscript. I would also like to thank Donald V. Helmberger for his suggestions and aid and Thomas H. Jordan and Bruce R. Julian for their comments and the use of their computer programs. I thank the National Science Foundation and the Beno Gutenberg Fellowship Fund for graduate fellowship support. 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. Contribution 2580 of the Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena. Published - Hart-1975-Journal_of_Geophysical_Research-_Solid_Earth__1978-2012_.pdf
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