QUANTIFICATION OF INTERPLATE COUPLING IN SUBDUCTION ZONES AND FORE-ARC TOPOGRAPHY

The effect of long term coupling in subduction zones on forearc topogr aphy is studied using a 2-dimensional finite element model. A curved f ault, representing the interface between subducting slab and overridin g plate, has been incorporated into a model with an elastic crustal la yer, a viscoelastic upper mantle, an initial topography and an effecti ve coefficient of friction on the fault. We assume that traction arisi ng from friction is one of the stresses acting on topography. For vari ous friction coefficients, the change of topography after some equilib ration time is computed with specific geometry and kinematic boundary conditions for three subduction zones: northern Chile, northern Japan and Tonga. While the intrinsic coefficient of friction for small rock samples is high (mu similar to 0.6 - 0.8), the observed topography of forearc regions are inconsistent with an effective friction coefficien t larger than 0.2.