Numerical Simulations Of Activities Of Fault And Study Of Seismology

In the first decade of the 21^th Century, human beings encountered two large disasters: one is 2004 Indian ocean tsunami arose from the Sumatra earthquake , the other is 2008 Wenchuan earthquake in China. We were reminded again that the earthquakes are still one of the most serious disasters in the future we will must face. Although many seismologists endeavored to forecast the earthquakes, it is still not sucessful. There are many reasons : one ? of these reasons is that we are not familiar with the mechanics of the earthquake preparation and the activities of the faults. In order to understand the behavior of the fault,this dissertation simulated the activities of fault by quasistatic finite element method (FEM) in thousands of years. We made use of the Contact technology of FEM to realize the interaction of the two parts of fault.The geometrical planar fault and geometrical bend fault all have been simulated and compared. The results show before a earthquake takes place, there will be a pre-slip which is resembled with experiments in laboratory .The different of activities of planar and bend faults are large: high heterogeneous stress distribution due to bend fault not only block the ruptures of median-small earthquakes, but also can gestate large earthquakes; high heterogeneous stress on fault also induce more foreshocks on bend fault than planar fault. The result of the bend fault model show the "characteristic earthquakes" distinctly, earthquakes repetition is quasiperiod. The earthquake frequence-size distribution of this "Characteristic earthquakes" is deviate from G-R relationship. These results are very useful to understand the behaviour of faults, furthermore, they provide good references for assessment of seismic risk.The G-R relation is a experiential formula based on statistic of lots of earthquakes in one region or global. Many researchers have given some explanations which are cited in this dissertation . Recently some researchers found a new type of earthquake activities of fault which is called "Characteristic earthquakes", this type is different from G-R relationship. Some typical examples of "Characteristic earthquakes" are introduced in this dissertation. The conflict of two types of earthquake activities is resolved by some numerical simulations: Characteristic earthquakes type is adapt to a single mature fault, G-R relationship type is adapt to earthquakes in a wide area. Then in order to explain the mechanism of "Characteristic earthquakes", the Kostrov's theory of dynamical rupture of earthquake is introduced. Some discussion and simulation results are given for more complex models.In the end of the dissertation , a simulation for 2001 Ms 8.1 Kunlunshan earthquake's dislocation is made. Different from inversion of dislocation, this model under a tectonic stress which can lead the Kunlunshan fault distort and rupture, the interactions of parts of the fault is still made use of Contact algorithm of FEM. Different from other simulation model in which pre-stress is designated on fault, the stress on the Kunlunshan fault of this model is spontaneously produced by interaction between the fault and the tectonic stress which surround the fault, this distribution of stress is closer to reality. The dislocation of simulation is quite consist with the data from satellite SPOT. From the result of the fault model, dislocation has a low value on one region on the fault near the Kusaihu , this is due to low stress drop during the earthquake ,the low stress drop is due to fault's tensile distortion. Klinger(2004) suggested the sub-fault of Kunlunshan fault caused the low dislocation on this region,but we believe that even not consider the effect of sub-fault, the high heterogeneous distribution of stress on fault due to fault distortion under a certain tectonic stress and friction probably is also a reasonable reason. By changing some parameters in the model, we calculate other models and compare them with each other. The method in the model can be easy to calculate the stress field of the fault and the area surround the fault.The effect of the heterogeneous stress distribution on fault which is caused by distortion of geometrical fault under certain tectonic stress and friction should be emphasized on earthquake simulations.