Geodynamics is the discipline that studies the mechanical properties of all kinds of mechanical process, power source and the medium of the earth’s large scale movement or integral movement, which is a branch of geophysics.
The mechanical phenomena occurring in the solid part of the earth are various, complicated in form and rich in content. The mission of the earth's dynamics is to analyze these phenomena, and to seek its mechanical mechanism through these phenomena, to grasp the laws of these phenomena and their changes, and to anticipate their future development trend. Therefore, must understand the mechanical characteristics of power source to promote and support these phenomena and the earth medium. The gravitational force of the earth itself is of course the long acting force of the tectonic movement, the diurnal and monthly tidal force, the inertia force caused by the earth rotation and oscillation must also be considered. Some of them are very small, but they can play a role in triggering tectonic movement. The thermal motion of the earth's interior forces and their viscosity must be considered.
The earth model is one of the foundations of the geodynamics. In the contemporary research on the geodynamics, the earth is usually regarded by people to consist of three parts: the crust, mantle and core. The ultimate goal of geodynamics is to understand the past, present and future behavior of the earth as a whole and the host system (the solar system), and understand these substances and environmental base for sustainable development for human survival.
Due to most of the problems of geodynamics are already aware of some of the mechanical consequences, and to seek their mechanical mechanisms and mechanical parameters, as well as to adjust or reconstruct the earth model. They are inverse problems in mechanics, so the solution is not unique. Human can only limit the change range of the solution according to enough experiment results to make a gradual reduction.
After 1970s, the theory of the geodynamics has developed rapidly. For example, theory of M.L.Smith - J.Wahr, takes the earth model as the basis, uses continuum medium mechanics method, takes the earth as the object, studies the earth nutation, earth tide and earth wave as a unity. The system of the theory is good; the results are consistent with the actual. With the development of the measurement and calculation technology, the precision of the inversion problem will be improved with the development of the theory of mathematics and mechanics. The geodynamics will play greater roles in elucidating earth structure formation and evolution.