Geochemical, petrologic and seismological observations indicate that there
may be high concentrations of water in the region above a subducting slab (
the mantle wedge), which could decrease the viscosity of the mantle locally
by several orders of magnitude. Using numerical models we demonstrate that
a low viscosity wedge has a dramatic influence on the force balance in a s
ubduction zone and leads to an observable signal in the topography, gravity
and geoid. A regional dynamic model of the Tonga-Kermadec subduction zone
shows that the viscosity of the wedge is at least a factor of 10 smaller th
an surrounding mantle lithosphere and asthenosphere. consistent with estima
tes from seismic dissipation and deformation experiments. (C) 2001 Elsevier
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