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  On the nature of P-n

Tittgemeyer, M., Wenzel, F., & Fuchs, K. (2000). On the nature of P-n. Journal of Geophysical Research: Solid Earth, 105(B7), 16173-16180. doi:10.1029/2000JB900061.

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Item Permalink: http://hdl.handle.net/11858/00-001M-0000-0010-CE45-5 Version Permalink: http://hdl.handle.net/11858/00-001M-0000-002C-2963-2
Genre: Journal Article

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 Creators:
Tittgemeyer, Marc1, Author              
Wenzel, F., Author
Fuchs, K., Author
Affiliations:
1MPI of Cognitive Neuroscience (Leipzig, -2003), The Prior Institutes, MPI for Human Cognitive and Brain Sciences, Max Planck Society, ou_634574              

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 Abstract: P,• phases are observed along many refraction seismic profiles and are common in earthquake records. Their velocities usually range from 7.8 to 8.2 km s-t. Classical ray theory used to interpret these observations implies a positive upper mantle velocity gradient. However, a wide spread positive velocity gradient in the lithospheric mantle is not expected from petrological and petrophysical data. Laboratory velocity measurements a.t elevated temparatures and pressures suggest positive velocity gradients only for very low heat flow values (_< 40 mW m-2). Higher heat flow causes negative gradients. Consequently, petrological models of the upper mantle would restrict Pn observations to Precambrian shields and old platforms, contrary to observations. We overcome this contradiction by considering media that contain random velocity fluctuations superimposed on positive or negative velocity gradients. In both cases, these structures generate Pn phases by wide-angle scattered waves. Short-wavelength random velocity fluctuations of only 0.5-1% superimposed on negative velocity gradients are sufficient for generating Pn phases. Consequently, this implies that an observed Pn wave does not necessitate a positive upper mantle velocity gradient. For a peridotitic upper mantle, fluctuations of this size can be explained by slightly varying the relative proportions of its minere[logical constituents. Anisotropy is likely to contribute to the inferred fluctuations.

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Language(s): eng - English
 Dates: 2000
 Publication Status: Published in print
 Pages: -
 Publishing info: -
 Table of Contents: -
 Rev. Method: -
 Identifiers: eDoc: 239070
ISI: 000088262000006
Other: P6624
DOI: 10.1029/2000JB900061
 Degree: -

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Title: Journal of Geophysical Research: Solid Earth
  Abbreviation : J. Geophys. Res. Solid Earth
Source Genre: Journal
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Publ. Info: Washington, DC, USA : American Geophysical Union
Pages: - Volume / Issue: 105 (B7) Sequence Number: - Start / End Page: 16173 - 16180 Identifier: ISSN: 2169-9313
CoNE: https://pure.mpg.de/cone/journals/resource/2169-9313