In-situ stress measurement of deep borehole in east of Hebei and its significance

In order to obtain the required basic information of crustal stress for exploitation and design of deepmine, Institute of Geomechanics of Chinese Academy of Geological Sciences carried out hydrofracturing in-situ stress measurements in three boreholes near Luanxian and Laoting fault in east of Hebei area successively in 2012 and 2013. The three boreholes are between 500—1 000 m in depth. The results of the stress measurements preliminarily revealed the distribution regularity of current in-situ stress in shallow crust of study area. The measured data show that the dominant direction of regional stress field is NW70°; the ratio of the maximum shear stress to the average stress of the three boreholes is in the range of 0.24—0.48 and the average values of the ratio are 0.30, 0.40, 0.30 for the three boreholes, which are less than 0.6，that is the friction limit state of earth’s crust stress. But the ratio got shortly after the Tangshan MS7.8 earthquake is large, few of them are greater than 0.6, and the average value is 0.44, which reveals that the stress accumulation degree in the study area was low and stress has been completely released. According to the friction criterion of faults and Byerlee law, the risk of a large seismic activity in the study area is in low risk.