Physics
Scientific paper
Oct 2004
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004georl..3119612n&link_type=abstract
Geophysical Research Letters, Volume 31, Issue 19, CiteID L19612
Physics
3
Geodesy And Gravity: Earth'S Interior-Dynamics (8115, 8120), Seismology: Core And Mantle, Tectonophysics: Stresses-General
Scientific paper
Recent observations of up to 6 secs of shear-wave splitting in deep focus earthquakes from the Tonga-Kermadec subduction zone provide insights into mantle dynamics near the 660 km discontinuity. Modeling of subduction body force stresses predicts large deviatoric stress (~40 MPa) in the topmost lower mantle below a viscosity increase at the 660 km discontinuity. Finite strain calculations produce significant amounts of natural strains (~7) in the lower mantle, and coherently aligned strain ellipses. For a viscosity model with a viscosity increase at 660 km, 5-10 secs of shear-wave splitting is predicted, compared to only 0-5 secs for uniform mantle viscosity. For a viscosity increase model, we predict that shear-wave splitting reduces from 7-10 secs to 4-6 secs when deformation above 410 km is ignored, and further reduces to 2-3 secs when deformation above 660 km is zeroed. Various conversions from finite strain to anisotropy have been explored. Predicted shear-wave splitting magnitudes are comparable to those observed from the Tonga-Kermadec subduction zone.
Kendall J.-Michael
Kusznir N. J.
Nippress Stuart E. J.
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