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Weak elastic anisotropy in global seismology

Leon Thomsen and Don L. Anderson
Weak elastic anisotropy in global seismology (in The interdisciplinary Earth; a volume in honor of Don L. Anderson, Gillian R. Foulger (editor), Michele Lustrino (editor) and Scott D. King (editor))
Special Paper - Geological Society of America (September 2015) 514: 39-50


It has been known for over 50 years that seismic anisotropy must be included in a realistic analysis of most seismic data. The evidence for this consists of the observed dependency in many contexts (reviewed briefly here) of seismic velocity upon angle of propagation and upon angle of S-wave polarization. Despite this well-established understanding, many current investigations continue to employ less realistic isotropic assumptions. One result is the appearance of artifacts which can be interpreted in terms of details of Earth structure rather than of the restrictive assumptions in the analysis.The reason for this neglect of anisotropy is presumably the greater algebraic complexity and the larger number of free parameters of anisotropic seismics. However, the seismic anisotropy in the Earth is usually weak, and the equations for weak anisotropy are only marginally more complex than for isotropy. Further, the additional parameters are commonly required to describe the data. Moreover, the parameters of weak anisotropy defined below (combinations of the anisotropic elastic moduli) are less subject to compounding of uncertainty and to spatial resolution issues than are the individual anisotropic moduli themselves. Hence inversions should seek to fit data with these parameters, rather than with those individual moduli. We briefly review the theory for weak anisotropy and present new equations for the weakly anisotropic velocities of surface waves. The analysis offers new insights on some well-known results found by previous investigations, for example the "Rayleigh wave-Love wave inconsistency", including the facts that Raleigh wave velocities depend not only on the horizontal SV velocity but also on the anisotropy, and Love wave velocities depend not only on the horizontal SH velocity but also on the anisotropy.

ISSN: 0072-1077
EISSN: 2331-219X
Serial Title: Special Paper - Geological Society of America
Serial Volume: 514
Title: Weak elastic anisotropy in global seismology
Title: The interdisciplinary Earth; a volume in honor of Don L. Anderson
Author(s): Thomsen, LeonAnderson, Don L.
Author(s): Foulger, Gillian R.editor
Author(s): Lustrino, Micheleeditor
Author(s): King, Scott D.editor
Affiliation: Delta Geophysics, Houston, TX, United States
Affiliation: Durham University, Department of Earth Sciences, Durham, United Kingdom
Pages: 39-50
Published: 20150904
Text Language: English
Publisher: Geological Society of America (GSA), Boulder, CO, United States
Number of pages: 13
References: 70
Accession Number: 2015-096605
Categories: Solid-earth geophysicsSeismology
Document Type: Serial
Bibliographic Level: Analytic
Annotation: Includes appendices
Secondary Affiliation: Universita degli Studi di Roma La Sapienza, ITA, ItalyVirginia Tech, USA, United StatesCalifornia Institute of Technology, USA, United States
Source Note: Online First
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Reference includes data supplied by the Geological Society of America, Boulder, CO, United States
Update Code: 201541
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