东构造结墨脱关键区域地应力场特征及其构造稳定性分析

为获取东构造结关键构造部位地应力特征、分析其构造稳定性，采用水压致裂法开展了墨脱断裂带西让段1个地应力孔、11个测试段的原位地应力测量工作。结果表明：61.43~121.34 m测试段最大、最小水平主应力值（SH、Sh）分别为3.05～14.50 MPa和2.16～9.87 MPa，垂向主应力值（Sv）为1.63~3.31 MPa，即SH>Sh>Sv；测点处应力场以水平挤压作用为主，均处于逆断层应力状态，且其主应力值随深度增加而逐渐增大，测点的最大水平主应力优势方位为北东东向；在整个地应力测量深度范围内，侧压系数值（Kav）为1.39~4.38，最大水平应力系数值（KHv）均大于1，且比值随深度的增加而增大，该关键部位区域应力场以水平应力为主导，方向性较强，所有测试段水平应力系数值（KHh）为1.23~1.66，与林芝−通麦段地应力特征参数计算结果基本相似；测点位置98 m以浅地层水平构造应力作用程度较小，应力积累水平较低，保持断层稳定所需的摩擦系数值小于实际断层的临界摩擦系数值，构造环境相对稳定，超过98 m深度地层由于水平构造应力起主要作用，保持断层稳定所需的摩擦系数值接近于实际断层的临界摩擦系数值，存在小概率发生断层失稳滑动的风险；区域强震在墨脱断裂带断层面上造成的左旋走滑方向上及逆冲方向上的库仑应力变化值的叠加量均为负值，抑制了断层的滑动，未能增加墨脱关键区域断层活动的危险性。

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

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.