Abstract After the May 12th, 2008 Wenchuan MS8.0 earthquake, series hydraulic fracturing in-situ stress measuring results indicate that the orientations of maximum principal stress, in the Beichuan, Pingwu and Guangyuan areas along the northeast segment of the Longmenshan fault belt, have deflected with values of 25°~69°, as compared with regional stress field. This phenomenon is also known as in-situ stress decoupling. It is found that the decoupling of maximum principal stress orientations is caused by the right lateral strike slipping activity of the northeast segment of the Longmenshan fault belt, and has a positive correlation with the strike slipping displacement of the fault. We explain this phenomenon and investigate the mechanism of the in-situ decoupling caused by the activity of the strike slip fault. Firstly, using the co-seismic right lateral strike slipping displacement boundary conditions of the Wenchuan MS8.0 earthquake fault, the disturbed stress field generated by the right lateral strike slipping is simulated with the method of two-dimensional finite element numerical simulation. Afterwards, the effect mechanism of disturbed stress on the regional stress field is deeply analyzed, combining the in-situ stress measuring results with the disturbed stress simulated results at typical boreholes. Preliminary results show that: (1) In-situ stress decoupling, particularly, the deflection of maximum principal stress orientations induced by the activities of strike slip fault, is generated by the influence of the disturbed stress field resulting from the fault slipping on the regional stress field. (2) The deflection angles of maximum principal stress orientations have a significant positive correlation with the strike slipping displacement, under the conditions of special length and frictional strength of the active fault. (3) The deflection angles of maximum principal stress orientations are very low in Baoxing, Yingxiu and Wenchuan areas, which are basically consistent with the regional stress filed. However, they are much higher in the regions of Beichuan, Pingwu and Guangyuan, which are respectively 65°, 56° and 29°, as well as having a basically positive correlation with the co-seismic right lateral strike slip displacement of northeast segment of the Longmenshan fault belt.
FENG Chengjun,ZHANG Peng,QI Bangshen et al. Mechanics of In-situ Stress Decoupling Caused by the Activity of Strike Slip Fault: The Case of Northeast Segment of Longmenshan Fault Belt[J]. jgg, 2017, 37(10): 1003-1009.
FENG Chengjun,ZHANG Peng,QI Bangshen et al. Mechanics of In-situ Stress Decoupling Caused by the Activity of Strike Slip Fault: The Case of Northeast Segment of Longmenshan Fault Belt[J]. jgg, 2017, 37(10): 1003-1009.
