Overriding Plate Velocity Control on Surface Topography in 2‐D Models of Subduction Zones

Abstract

AbstractWe study the dynamically induced flexural topography in subduction numerical mechanical models. We focus on the topographic changes at the overriding plate (OP) surface induced by variations in OP kinematics, particularly when the subducting plate (SP) has a stationary motion after having reached the rigid base of the upper mantle. Our models consist of two viscoelastic plates with free surfaces and an isoviscous mantle. Friction is imposed along the planar subduction interface. We first characterize the main topographic features at a constant OP velocity, using spatial definitions based on geometrical estimations of the volcanic arc position. The models exhibit the formation of a bulge in the forearc area followed landwards by a depression and a smaller second bulge, both bracketing the arc region. The steady‐state distance to the trench of these features increases with OP velocity. Their amplitude is affected by the far‐field OP tectonic regime that depends on kinematics, and plates and subduction interface strength. We next test the effect of sudden changes in OP velocity. An OP acceleration yields a transient topographic tilt, during which the outer forearc quickly subsides whereas the arc region uplifts, and that is followed by reverse slower motions. An OP slowdown induces opposite motions. The rates of elevation change during the tilt are approximately proportional to velocity variations and mainly sensitive to the SP strength. The rates are higher than 0.1 mm/yr for velocity changes higher than 1 cm/yr. We suggest that topographic accommodations of OP velocity changes should be considered when quantifying nonisostatic topography.