Research Of Active Fault And Numerical Analysis Of Regional Modern Tectonic Stress Field In Changchun

The earthquake is a kind of unplanned natural disaster,which could give a huge disaster and hazard to the humam society. The active fault is closely related to the moderately srong earthquake,and the earthquake disaster in city is mainly induced by the active fault moving abruptly and fastly underlying city. A great many of earthquake examples express that,the active fault not only is the source of earthquake,but also is the main reason to aggravate damage. Changchun city located in combining site of mountain area and plain in the geological structure lies in a side of basin on the edge of ZhangGuangCai ridge and Song Liao basin. In the research area there are a series of fractures,among which a NE-NNE fracture is the main structure ,however, a NW fracture and a SN fracture are secondary. The NE fracture and the NW fracture intersect each other to form the middle strength of seismic activity zone. With the rapid development of economy and the progress of construction in Changchun city,it is very important to comprehensively and scientifically proof the geological environment and the earth stability,and to properly predict influence on engineering construction and economy environment by geological environment.This text on the basis of analysing and generalizing the data and the spot investigation,under comprehensively considering average slip rate of fault and average recurrence periodic time of earthquake,each main active fault in the research area was separately evaluated for its activity by evaluating standard for activity of fault,and evaluation result indicated that the activity of fault was weak. At the same time the segmentation analysis and the fractal calculation for the fault system and its main active faults in the research area had been finished separately. Result of segmentation indicated that every main active fault in the research area had the clear segmentation characteristic,and geometric shape of each segment is less different each other,but its activity is no so,for example,fault called KaiYuanBao-XiaoChengZi is composed of the mutually independent WuJiaZi-ZhuJiaWoBao segment and ZhuJiaWoBao- XiaoChengZi segment,with the linear spread,the less secondary fracture and the simple geometric structure,however,the activity of WuJiaZi-ZhuJiaWoBao segment with relation to FanJia-Tun earthquake 5.2 is more strong than ZhuJiaWoBao- XiaoChengZi segment. In the research area the result of fractal calculation and its relevant check indicated that fault system had the very good statistic self-similarity and fractal feature,and much smaller value of fractal calculation showed that faults with simple structure,weak tectonic activity and earthquake in the area were lack of branch fracture and secondary fracture. Consequence with correspondence to the spot investigation declared that fractal value could be considered as an aggregative indicator for quantitatively assessing the complexity degree and the activity of fracture.On the basis of regional geological analysis,actual data about crustal stress,comprehensive fault plane solution of single small earthquake and source mechanism solution in the research area,regional modern tectonic stress field was analysed through finite element programming,and the analytical result indicated that in the regional stress field distribution for primary stress was controlled by fault zone,with stripped centralizing and apparent concentration phenomenon of stress appears along YiSu fault,YiTong River fault and DongLiao River fault ect.,of which stress concentration mainly appeared on the end and crossing;Obvious fluctuation for shear stress also appeared along fault zone,with apparent concentration appearing along each sector like GongZhuLing,JingTai and FanJiaTun ect. of strongly active fault called YiShu,as meets the fact. Therefore,it is showed that,under the clear geological background of the region,the full and accurate data along with the proper calculation model,numerical modelling by the finite element method could relatively accurately reflect the characteristic of tectonic stress field of the region,which provided the certain means for evaluation for the activity of fracture.