A no-net-rotation model of present-day surface motions

A significant portion of the Earth's surface consists of zones of diffuse d eformation. The interior regions of these diffuse zones of deformation move at distinctly different velocities from that of adjacent plates, and, beca use of their complexities, have been ignored in previous no-net-rotation (N NR) models. We have calculated a new NNR model from a continuous velocity f ield that incorporates both rigid plate motion and velocity gradients withi n plate boundary zones. When compared with earlier NNR models we find signi ficantly different angular velocities for many plates. Differences between the NNR model presented here and earlier NNR models can be attributed to th e effect of including velocity gradients in diffuse plate boundary zones as well as to the actual differences between geodetically derived surface mot ions and geologic estimates.