The Effects of Viscous Stresses and Mantle Velocities on Subduction; Finite Difference Modeling

This thesis presents a two-dimensional finite-difference model of subduction, which is used to explore the characteristics of subduction that are most closely related to deformation in the overriding plate. The model focuses on how the angle, a, at which the slab subducts and the rate, Vr, at which the subduction boundary "retreats " are affected by the negative buoyancy of the subducting lithospheric slab and the viscous forces that arise where the mantle and subducting slab are in motion relative to one another. The viscous forces acting on the slab are approximated as the product of the viscosity, p = 1021 Pa- s, and the relative velocity of the subducting lithosphere and the surrounding mantle, divided by y, the length-scale over which these viscous forces might operate. The model treats the normal and shear viscous forces seper-ately; the normal viscous force is equal to the slab-perpendicular component of the relative velocity times A-, whereas the shear viscous force equals the slab-parallel 7N&apos