The Research Of The Regional Stress State And Faultmechanics Significance Of The Middle Segment Of Tan-lu Fault

Firstly, this paper collects the geological structure data of the middle segment of Tan-Lu Fault; conducts fine geological survey in the study area with the new borehole TV; discover the geological background of the study area comprehensively. Secondly, this paper obtains and analysis the stress data of the study area with hydraulic fracturing method and CBDM method. Thirdly, the characteristic stress indexes used to analyze fault strength are summarized, including α which represents the angle between the direction of major stress and fault plane, μm which implies the stress accumulation level, and analyze the fault strength characteristic of the middle segment of Tan-Lu Fault according to the stress data. Then, analyze the deep fault strength characteristic according to the characteristic stress indexes with the earthquake mechanism of the small earthquake in the middle segment of Tan-Lu Fault. Finally, simulating the activity of the middle segment of Tan-Lu Fault with 3DEC code, and discussing the relationship between the stress state and fault strength.Based on the above research, we come to the following conclusions.(1) The occurrence of the structural plane in the study area is affected by the concealed fault, above which the dip of the structural plane is SN, and angle of dip is about 60°, the same to the occurrence of the fault plane; below which the dip of the structural plane is NE, and angle of dip is about 60°, as a result of mutual influence of the Tan-Lu fault and the concealed fault.(2) The research obtains several groups of accurate stress data using the optimized hydraulic fracturing method. The result shows that the mean direction of the maximum horizontal major stress is N84.1°E, the relationship of the three principal stress is SH> Sh > Sv,the fault performs as a reverse fault.(3) The angle between the direction of maximum major stress and fault plane of the middle segment of Tan-Lu Fault is 64.1°~74.1°(>2α*), so the friction coefficient of fault is low, and the fault is weak compared with the brittle crust. The stress accumulation level indexes μm in the study area is 0.48, which shows the stress accumulation level in the area is high, and the crust is in its limit state.(4) The μm of the middle segment of Tan-Lu Fault between 0.2 and 0.4 mainly lies on the south of the study area, where the frequency of small earthquake is high, informs that the stress can’t accumulate. The μm larger than 0.4 mainly lies on the the study area and the north of the study area, indicates that the fault is on close state, the stress accumulate a lot, the possibility of huge earthquake in the area is getting higher.(5) According to the stress state and fault friction coefficient of the middle segment of Tan-Lu Fault, then simulating with 3DEC code, we find that when the compass stress with direction EW arising, the stress increment in the east of the middle segment of Tan-Lu Fault is higher than the west, the possibility of happening earthquake in the east may higher than west.