Physics of the Earth and Planetary Interiors, 147(1), 59-77, doi:10.1016/j-pepi.2004.06.011, 2004
Possible effects of lateral viscosity variations
induced by plate-tectonic mechanism
on geoid inferred from numerical models of mantle convection
Masaki Yoshida
Abstract
In a traditional analytical method,
the convective features of the Earth's mantle have been inferred
from surface signatures obtained by the geodynamic model
only with depth-dependent viscosity structure.
The moving and subducting plates, however, bring
lateral viscosity variations in the mantle.
To clarify the effects of lateral viscosity variations
caused by the plate-tectonic mechanism,
I have first studied systematically instantaneous dynamic flow calculations
using new density-viscosity models only with vertical viscosity variations
in a three-dimensional spherical shell.
I find that the geoid high arises over subduction zones only when
the vertical viscosity contrast between the upper mantle and the lower mantle
is O(103) ～ O(104), which seems to be much larger
than the viscosity contrast suggested by other studies.
I next show that this discrepancy may be removed when
I consider the lateral viscosity variation caused by
the plate-tectonic mechanism
using two-dimensional numerical models of mantle convection
with self-consistently moving and subducting plates,
and suggest that the observed geoid anomaly on the Earth's surface
is significantly affected by plate-tectonic mechanism as a first-order effect.