The writer published in 1967 the idea that tectonic movements or crustal deformations are generally characterized by uniform rates or velocities, for long time more than 100 years. For short time less than 100 years, the movements may be accumulations of some stochastic processes including earthquakes.
The real tectonic movements for long time can be approximated to the movement of ideal viscous fluid, under a stationary deviatoric stress. This approximation is also probable for the case of a glacier flowing down in a valley, only by its own weight. The regional stress field associated with the tectonic movements appears to be related to the subduction by weight of oceanic lithosphere, at least in the island-arc areas. Consequently, the ultimate cause of stationary tectonic movements might be the gravity of the earth.
