Open AccessConstraining seismic velocity and density for the mantle transition zone with reflected and transmitted waveforms
Author(s) -
Lawrence Jesse F.,
Shearer Peter M.
Publication year - 2006
Publication title -
geochemistry, geophysics, geosystems
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.928
H-Index - 136
ISSN - 1525-2027
DOI - 10.1029/2006gc001339
Subject(s) - geology , discontinuity (linguistics) , transition zone , mantle (geology) , density contrast , seismology , parameterized complexity , classification of discontinuities , geodesy , geophysics , physics , mathematics , astrophysics , mathematical analysis , combinatorics
We examine stacks of several seismic phases having different sensitivities to mantle transition zone structure. When analyzed separately, underside P and S reflections ( PdP and SdS ) are suggestive of very different structures despite similar raypaths and data coverage. By stacking the radial component of PdP rather than the vertical PdP , we show that this difference does not result from interference from other more steeply inclined phases such as PKP and Ppdp diff . In general, stacks of P ‐to‐ S converted phases ( Pds ) appear to lack evidence of a 520‐km discontinuity when examined without other phases. When these phases and stacked topside P reflections ( Ppdp ) are analyzed jointly using a nonlinear inversion method, consistent but nonunique, seismological models emerge. These models show that a discontinuity at ∼653 km depth has smaller contrasts in density and velocity than found in most previous studies. A sub‐660 gradient can account for the majority of this difference. A 1.6 ± 0.5% P ‐velocity contrast and a 2.2 ± 0.3% density contrast at ∼518 km depth without a S ‐velocity contrast can explain the lack of a P 520 s , together with robust Pp 520 p and S 520 S phases. For models parameterized with a finite thickness for each discontinuity, the 410‐km discontinuity is consistently ∼3 times thicker than the 660‐km discontinuity.