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Even-degree lateral variations in the Earth's mantle constrained by free oscillations and the free-air gravity anomaly

Ishii, Miaki and Tromp, Jeroen (2001) Even-degree lateral variations in the Earth's mantle constrained by free oscillations and the free-air gravity anomaly. Geophysical Journal International, 145 (1). pp. 77-96. ISSN 0956-540X. doi:10.1111/j.1365-246X.2001.00385.x.

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The recent occurrence of several large earthquakes, in particular the 1994 June 9 Bolivia event, has motivated a re‐examination of the Earth's large‐scale heterogeneity from a normal‐mode or free‐oscillation perspective. Compared to earlier studies, the number of normal‐mode constraints on lateral variations in the mantle has increased five‐fold, and toroidal and cross‐coupled modes complement the traditional spheroidal mode data set. It is demonstrated that this large collection of mode data, combined with the free‐air gravity anomaly, can reliably constrain even‐degree lateral variations in wave velocities as well as density. We present the first whole‐mantle density model constrained by seismology. Our shear and compressional velocity models are consistent with existing models based upon traveltimes and waveforms, and are reasonably well correlated throughout the mantle. Shear and bulk sound velocity models exhibit a gradual decrease in correlation with depth, and are anti‐correlated near the core–mantle boundary. We find that lateral variations in density are poorly correlated with wave velocities, and are locally anti‐correlated with shear velocity in the lowermost mantle. The correlations between wave velocities and density suggest both a thermal and a compositional origin to lateral heterogeneity. In addition to traditional maps of lateral variations in wave velocity, we also present maps of lateral variations in shear and bulk moduli. The inversion puts weak constraints on even‐degree topographic variations on the core–mantle boundary, the 660 km discontinuity and dynamic free surface topography. Finally, we determine both radially and laterally varying scaling relationships, including Poisson's ratio.

Item Type:Article
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URLURL TypeDescription
Tromp, Jeroen0000-0002-2742-8299
Additional Information:© 2001 RAS. Accepted 2000 September 21. Received 2000 June 7; in original form 1999 November 16. Published: 01 April 2001. We wish to thank R. J. O’Connell, Svetlana Panasyuk, Jerry X. Mitrovica, Hendrik Jan van Heijst and Guy Masters for numerous discussions and suggestions. We also thank Jeffrey Park for a constructive review. This research was supported by the David and Lucile Packard Foundation. MI was also supported by a Natural Sciences and Engineering Research Council of Canada Postgraduate Scholarship.
Group:Seismological Laboratory
Funding AgencyGrant Number
David and Lucile Packard FoundationUNSPECIFIED
Natural Sciences and Engineering Research Council of Canada (NSERC)UNSPECIFIED
Subject Keywords:density, free-air gravity, free oscillations, Poisson’s ratio, seismic tomography, seismic velocities
Issue or Number:1
Record Number:CaltechAUTHORS:20171204-145544102
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Official Citation:Miaki Ishii, Jeroen Tromp; Even‐degree lateral variations in the Earth's mantle constrained by free oscillations and the free‐air gravity anomaly, Geophysical Journal International, Volume 145, Issue 1, 1 April 2001, Pages 77–96,
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:83670
Deposited By: Tony Diaz
Deposited On:13 Dec 2017 05:08
Last Modified:15 Nov 2021 20:13

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