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Properties of the core-mantle boundary and observations of PcP

1968; American Geophysical Union; Volume: 73; Issue: 18 Linguagem: Inglês

10.1029/jb073i018p05901

2156-2202

Goetz G. R. Buchbinder,

Geological and Geochemical Analysis

Journal of Geophysical Research (1896-1977)Volume 73, Issue 18 p. 5901-5923 Properties of the core-mantle boundary and observations of PcP Goetz G. R. Buchbinder, Goetz G. R. BuchbinderSearch for more papers by this author Goetz G. R. Buchbinder, Goetz G. R. BuchbinderSearch for more papers by this author First published: 15 September 1968 https://doi.org/10.1029/JB073i018p05901Citations: 33AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onEmailFacebookTwitterLinkedInRedditWechat Abstract Study of PcP phases from eight explosions and three earthquakes shows that the initial direction of motion of PcP reverses at an epicentral distance of about 32° and that PcP amplitudes pass through a minimum at this distance. The effects are caused by properties of the core-mantle boundary. Calculations of reflection coefficients at a plane solid-liquid boundary show that a model with P and S velocities at the bottom of the mantle of 13.64 km/sec and 7.30 km/sec, respectively; with a P velocity at the top of the core of 7.5 km/sec; and with a ratio of core density to mantle density of 1.0 will satisfy the observations of amplitude and change of initial phase of PcP. A range of similar models with velocities at the top of the core down to 7.2 km/sec and density ratios as high as 1.05 will also satisfy the observations. Amplitude observations of PKKP phases also satisfy the model. The new structure is in sharp contrast to the structure of conventional models that have a core velocity of about 8.1 km/sec and a density ratio of about 1.7, but such models will not satisfy the new data. One way to reconcile the new structure near the core-mantle boundary with other relevant information is to assume a model in which the lowermost mantle is inhomogeneous. The inhomogeneity is caused by an increase in iron or other heavy metal content with depth, which increases the mean atomic weight and the density with little change in P velocity. The drop in P velocity across the core-mantle boundary may then be explained by a step increase in mean atomic weight with little change in density. The Adams-Williamson equation will not be valid in the regions in which the changes in density and mean atomic weight are postulated. The incompressibility is not continuous across the core-mantle boundary. PcP travel-time observations do not permit resolution of irregularities at the core-mantle boundary of less than about 5° in slope and about ±5 km in height. The scatter of the observed travel times from a least-squares fit does not indicate slopes of over 6° or elevation differences much over 5 km on the core-mantle boundary. References Alder, B. J., Is the mantle soluble in the core?, J. Geophys. Res., 71, 4973–4979, 1966. Alexander, S. S., R. A. Phinney, A study of the core-mantle boundary using P waves diffracted by the earth's core, J. Geophys. Res., 71, 5943–5958, 1966. Anderson, D. L., R. L. Kovach, Attenuation in the mantle and rigidity of the core from multiply-reflected core phases, Proc. Natl. Acad. Sci., 51, 168–172, 1964. Anderson, O. L., Seismic parameter Ø Computation at very high pressure from laboratory data, Bull. Seismol. Soc. Am., 56, 725–731, 1966. Båth, M., The density ratio at the boundary of the earth's core, Tellus, 6, 408–414, 1954. Berg, E., S. 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Am., 44, 39–55, 1954. Pekeris, C. L., The internal constitution of the earth, Geophys. J., 11, 85–132, 1966. Phinney, R. A., S. S. Alexander, P-wave diffraction theory and the structure of the core-mantle boundary, J. Geophys. Res., 71, 5959–5975, 1966. Rykunov, L. N., P waves diffracted at the earth's core and rigidity of the core, English Transl., Izv. Akad. Nauk. SSSR, Ser. Geofiz., 678–684, 1959. Sacks, S., Diffracted wave studies of the earth's core, 1, Amplitudes, core size and rigidity, J. Geophys. Res., 71, 1173–1181, 1966. , Seismological Service of Canada, Seismological Bulletin, Seismological Series of the Dominion Observatory, 1967. , United States Coast and Geodetic Survey, Handbook Worldwide Standard Seismograph Network, prepared forUnited States Coast and Geodetic Survey,Washington, D. C.,1964. Citing Literature Volume73, Issue1815 September 1968Pages 5901-5923 ReferencesRelatedInformation