Analysis of in-situ stress field characteristics and tectonic stability in the Motuo key area of the eastern Himalayan syntaxis

• Published in: Dizhi lixue xuebao
• Main Authors: ZHANG Bin, SUN Yao, MA Xiumin, PENG Hua, JIANG Jingjie, MAO Jiarui, ZHANG Wenhui, ZHAI Yudong
• Format: Article
• Language: Chinese
• Published: Institute of Geomechanics, Chinese Academy of Geological Sciences 2023-06-01
• Subjects: eastern himalayan syntaxis; hydraulic fracturing; in-situ stress measurements; in-situ stress field characteristics; tectonic stability
• Online Access: https://journal.geomech.ac.cn//article/doi/10.12090/j.issn.1006-6616.20232908

In order to obtain the in-situ stress field characteristics and analyze tectonic stability in the Motuo key area of the eastern Himalayan syntaxis, the in-situ stress measurement of one in-situ stress hole and 11 test sections of the Xirang section of the Motuo fault zone were carried out by the hydraulic fracturing method. The results show that the maximum and minimum horizontal principal stress values (SH, Sh) in the test section of 61.43−121.34 m are 3.05−14.50 MPa and 2.16−9.87 MPa, respectively, and the vertical principal stress values (Sv) are 1.63−3.31 MPa, namely, SH>Sh>Sv. The in-situ stress field at the measuring point is dominated by horizontal compression, and all of them belong to the in-situ stress state of reverse fault. The principal stress values gradually increase with the increase of depth, and the dominant direction of the maximum principal stress is NEE. In the whole range of in-situ stress depth, the lateral pressure coefficients (Kav) are 1.39−4.38, the maximum horizontal stress coefficients (KHv) are greater than 1, and the ratio increases with the increase of depth. The regional stress field of this key area is dominated by horizontal stress and it is highly directional. The horizontal stress coefficients (KHh) of all test sections are 1.23−1.66, which are similar to the calculation results of in-situ stress characteristic parameters in Linzhi−Tongmai section. The horizontal tectonic stress of the shallow level at 98 m is relatively small, and the stress accumulation level is low. The friction coefficient required to maintain fault stability is smaller than the critical friction coefficient of actual fault, and the tectonic environment is relatively stable. When the depth exceeds 98 m, the friction coefficient required to maintain fault stability is close to the critical friction coefficient value of the actual fault due to the dominant role of horizontal tectonic stress, and there is a small risk of fault instability slip. The superposition of the Coulomb stress change in the sinistral strike-slip direction and the thrust direction caused by the strong regional earthquakes on the fault plane of the Motuo fault zone in the study area are all negative numbers, which inhibits fault slip and does not increase the risk of fault activity in the study area.