Garnero, Edward J. and Helmberger, Donald V. (1995) On seismic resolution of lateral heterogeneity in the Earth's outermost core. Physics of the Earth and Planetary Interiors, 88 (2). pp. 117-130. ISSN 0031-9201. http://resolver.caltech.edu/CaltechAUTHORS:20121205-104754253
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Issues concerning resolution of seismically determined outermost core properties are presented with an example from three earthquakes in the Fiji-Tonga region. Travel time behavior of the commonly used family of SmKS waves, which travel as S in the mantle, P in the core, reflecting m − 1 times at the underside of the core-mantle boundary (CMB), are analyzed over a large distance range (125–165°). Data having wavepaths through an area of known D″ heterogeneity (±2%) exhibit systematic anomalies in SmKS differential times. Two-dimensional wave propagation experiments demonstrate how large-scale lower-mantle velocity perturbations can explain long-wavelength behavior of such anomalous SmKS times, though heterogeneity on smaller scales may be responsible for the observed scatter about these trends. If lower-mantle heterogeneity is not properly accounted for in deriving a core model, misfit of the mantle model maps directly into core structure. The existence of outermost core heterogeneity is difficult to resolve at present, owing to uncertainties in global lower-mantle structure. Resolving a one-dimensional chemically stratified outermost core also remains difficult, owing to the same uncertainties. Inclusion of the slowly accruing broadband data should help in this regard. Restricting study to higher multiples of SmKS (m = 2, 3, 4) can help reduce the effect of mantle heterogeneity, because of the closeness of the mantle legs of the wavepaths. SmKS waves are ideal in providing additional information on the details of lower-mantle heterogeneity.
|Additional Information:||© 1995 Elsevier Science B.V. Received 3 February 1994; revision accepted 19 July 1994. We thank Steve Grand for useful discussions, and two anonymous reviewers for helpful comments. Lian-she Zhao helped in 2-D model parametrization. This research was supported by NSF Grant EAR-91-17781. This paper is Contribution 5374, Division of Geological and Planetary Sciences, California Institute of Technology.|
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|Official Citation:||Edward J. Garnero, Donald V. Helmberger, On seismic resolution of lateral heterogeneity in the Earth's outermost core, Physics of the Earth and Planetary Interiors, Volume 88, Issue 2, March 1995, Pages 117-130, ISSN 0031-9201, 10.1016/0031-9201(94)02976-I. (http://www.sciencedirect.com/science/article/pii/003192019402976I)|
|Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Ruth Sustaita|
|Deposited On:||05 Dec 2012 19:32|
|Last Modified:||05 Dec 2012 19:32|
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