In‐Situ Stress Measurement and Tectonic Stress Field in the Lanzhou‐Maqu Region of China

The study region is a strongly deformed frontal area of the Tibet plateau caused by the northeastward compression of Indian plate. The study on the present tectonic stress field in this region has important meaning for the research of continental dynamics. The values and directions of the ground stress at several sites of Lanzhou-Maqu area are given in the paper using piezomagnetic stress gauge overcoring method. The measurement sites are situated in Ayishan, Dashui, Gahai, Ma'ai, and Qingshui. The previous stress data are also analyzed for systematically studying the tectonic stress field in the region of Lanzhou-Maqu and its adjacent area. The result shows that the values of ground stress in depths of tens meters are medium as compared to that in other areas, and increase with depth, the increase rate differs in different tectonic units. The overall direction of maximum horizontal principal stress is northeast with a small variation in different tectonic units. The direction of maximum horizontal principal stress is nearly west-east in Ordos block, NNW-NE in Hexizoulang. The direction of maximum principal stress changes considerably in the southeast part of Qilanshan Mountains. The west Qinling Mountain is a transition zone of ground stress. The direction of maximum horizontal principal stress changes gradually from NE in the north to EW in the middle and SEE in the south part. The results agree with the strain field in this area from GPS observation.