Dynamic Combination Of Crust Block And Migration Of Major Region Of Earthquake

China is the country which has the most of continental strong earthquakes. There is 33% earthquakes in world happened in China which just has 7% area in world. According to the special tectonic background and dynamic condition of continental earthquakes, scholars from home and abroad have deeply researched the character of continental earthquakes and the mechanism of earthquakes(Molnar P,1975;Tapponnier et al,1982,1988;Zoback et al.,1989), thought that strong continental earthquakes has correlation with different active blocks (Zhang, 1984; Ma, 1989; Ding et al., 1989). Moreover, Ma (1999) thought that we should transfer our concentration to active block from active faults, and she emphasized the importance of active block in earthquake research. The relation between active blocks and earthquakes will be an aspect of earthquakes prediction research.According to active blocks, this paper researched the relation between active combination of blocks and the character of distribution of main region of strong earthquake action using finite element numerical simulation method. First, put forward the theory of combination pattern of active blocks, simulated and analyzed the effect of combination pattern of active blocks to the distribution of stress, and concluded the rules. Then aimed at the area of southwest China, designed a model of Tibetan Plateau crust which consists of six blocks, studied the influence of the combination pattern of second grade blocks in this area to the main body of strong earthquakes through comparing and analyzing the three tiny dynamic stages and also concluded the rules. The details of the research and conclusion we get as follows:1. The theory of the combination pattern of blocks: the combination pattern of active blocks is the relation among the blocks. In term of the arrangement mode of blocks, there are parallel arrangement mode, nested arrangement mode and irregular arrangement mode. In term of the medium structure, there are three mode among blocks which are consolidation, off-coupling and weak coupling.2. the conceptual model of combination blocks: designed parallel arrangement mode and nested arrangement mode, gave compression and shearing boundary condition, and then concluded the rules of stress accumulating, transferring and reallocating; If the relation among blocks transfer to consolidation from weak coupling, the activity will become weak, but the whole stress increased, so the seismic risk along the boundary of the combination blocks is higher; In opposite, if the relation among blocks transfer to weak coupling from consolidation, the activity will become stronger, and the shear tress is easy to focus on the fault between blocks.3. The analysis about the tiny dynamism and main region of earthquakes in southwest area: according to the result of Hong et al (2000), we extended the partition of tiny dynamism to 2008yr, and designed a model of Tibetan Plateau crust which consists six active blocks. We aimed at southwest China, chose three tiny dynamical stages to simulate and analyze, and demonstrated the influence of the mode of combination blocks to the distribution of strong earthquakes.4. Advancing"forward method"numerical simulating idea: according to the distribution character of previous earthquakes to analyses the combination modes and active tendency of the blocks. Then, to analyze the boundary action of surrounding tectonic or blocks in the basis of the mechanical properties of earthquakes, calculating the stress distribution under this kind of combination mode and boundary action with finite element numerical simulating method; Aside, comparing the distribution character of the main region of strong earthquakes in this tiny dynamic stage with the result we got .5. Discussion:In every tiny dynamic stage, active blocks have theirs own special combination modes. In some stage, the most of the blocks concrete together (such as the tiny dynamic stage of 1914-1927yr), and as a whole to transfer the stress. In some stage, one of the blocks will have the strongest activity (such as the tiny dynamic stage of 1993-2008yr), this block changes the stress concentration modes of the different margins with special movement under the effect of the boundary condition. Therefore, the research about the combination mode of active blocks can explain the stress concentration mode along the boundary of the active blocks (or several active blocks which had been consolidated as a whole), and then deepen the understanding of the distribution character of the main region of strong earthquakes.Through analyzing the mechanism properties of the earthquakes that above Ms7, we find that the most of the earthquakes happened in some tiny dynamic stage have similar mechanical explanation, that's may be strike-slip, or may be compression, which embodies the stability of the tectonic action in a tiny dynamic stage. The motion of the active blocks or the action among blocks is the reregulation for getting a more stable stage.The pushing action that Eurasia plate suffered from India plate is very complex and hard to forecast, and the combination modes of the second grade blocks in Tibetan plateau should also according to analyzing the mechanical properties of previous earthquakes and the field research of active faults, so the earthquake prediction will still be a formidable mission and a great challenge. Wish the idea we put forward would be good for explaining the distribution character of the strong earthquakes.