Abstract: Plate dynamics is an important topic in geodynamics research. In this paper, the driving forces for current lithospheric plates are studied based on the principle of torque balance for stable moving rigid bodies. A method for identifying plate driving forces by calculating the angle between the torque and the plate angular momentum is proposed, and the stability of rigid plates is quantitatively analyzed under the constraint of the viscous resistant shear forces acting on the bottom of the plates. Furthermore, the moments of inertia as well as the angular momentum are computed for each plate in terms of the latest lithospheric structure model and absolute plate motion model, and the boundary and basal torques are obtained for the plates based on simple physical models. The results show that the residual torque that balances the ridge and the basal torques may be explained by those originated from the subduction slabs, collision zones, and rift zones, and that the ridge and slab forces are the main driving forces for plate motions, while the inter-plate collision are important driving forces for the Eurasian plate.

Key words: plate tectonics, driving forces, torque balance, basal shear