Record details

Title
    Inference of viscosity from the oceanic geoid : Indication of a low viscosity zone below the 660 km discontinuity
Statement of responsibility
    Kido Motoyuki, Ondřej Čadek
Author
    Čadek, Ondřej
    Motoyuki, Kido
Language
    anglicky
Source title - serial
    Earth and planetary science letters
Vol./nr.
    Vol. 151, no. 3-4
Pages
    p. 125-137
Year
    1997
Notes
    7 obr., 2 s.bibl.
    Zkr. název ser.: Earth planet. Sci. Lett.
Subject group
    astenosféra
    diskontinuita
    geoid
    plášť
    proudění konvekční
    seizmologie
    tomografie
Keyword
    660
    Below
    Discontinuity
    Geoid
    Indication
    Inference
    Km
    Low
    Oceanic
    Viscosity
    Zone
Abstract (in english)
   We have attempted to infer details of the viscosity structure in the top 1000 km of the mantle from the geoid and tomographic structure beneath the oceans. In order to eliminate the gravity signal from problematic masses located below the subduction zones and the continents, we have considered only the intermediate degrees of the oceanic geoid (l=12-25). A genetic algorithm has been used to determine the family of viscosity models which give the best correlation with the observed geoid. Our inversion clearly identifies the astenosphere just below the lithosphere and also confirms the viscosity increase in the lower mantle predicted by previous inferences, but suggests that the main viscosity jump occurs at a depth of about 1000 km and not at the usually stated 660 km boundary. Somewhere in the depth range of 400-1000 km, a low viscosity zone may exist where the viscosity decreases to a value comparable with the asthenosphere.
   Existence of such a low viscosity zone is supported by recent analysis of deep mantle anisotrophy which flavours a flow pattern with a strong horizontal component in the top part of the lower mantle. Unfortunately, the resolution of the inversion as well as the quality of recent seismic tomographic models are not sufficient to localize the depth and to come up with a higher accuracy for the viscosity of this low viscosity channel
Contributor
    Česká geologická služba
Contributor code
    ČGS (UNM)
Source format
    U
Entered date
    21. 2. 2008
Import date
    8. 8. 2012