DISCUSSION ON DRIVING FORCES AND MECHANISMS OF EARTHQUAKES IN CHINA FROM THE VIEWPOINT OF EARTH'S CRUST DYNAMICS
This paper considers mainly the contradiction between the gravitational force and heat energy as a guidence dealing with the occurring of earthquakes in China and their mechanisms from the angle of both energy transformation and material transportation. Although earth rotation, gravity and heat energy are major driving forces to produce tectonic activities and seismicities, but the first one is just regarded as a long-term acting force for slow motion of its interior materials, the second acts as a force to keep the earth in equilibrium, and the third may cause the crust break up abruptly and may destroy the gravity isostasy accompanied with lateral sliding due to gravitational rheology which is only responsible for shallow earthquakes and superficial tectonic activities. Therefore, both time-and space-dependent movements of earth material may be horizontal or vertical in phenomena controlled by the characteristics of acting forces.Generally, the state of tectonic stress can directly be influenced by the subduction of oceanic plate at island arc structures or of one continent underneath the another only within relatively narrow zones adjacent to the subduction belts, and the earthquake mechanisms along them may be subjected to frictional sliding or stick-slippage. Most of sedimentary basins and grabens in China with characteristics of abnormally high heat flow, positive gravity isostasy and thin crust appear to have developed since Mesozoic and Cenozoic, it reflects that large-scale vertical motions, strong in the past and weak nowadays, are driven by the upward flow of materials in upper mantle beneath these basins and grabens. This sort of vertical motion are responsible to compensate the materials imposed by the lateral motions which are induced indirectly by descending plate into upper mantle. Thus the driving forces and mechanisms of earthquakes occurred at these edges of the basins and grabens should be different form those at subduction belts.