南迦巴瓦地区地应力场估算与构造稳定性探讨

南迦巴瓦地区是喜马拉雅东构造结新构造活动最为强烈的区域, 晚第四纪活动断裂发育, 地震活动强烈, 嘉黎断裂带、东久-米林断裂带及墨脱断裂带等活动断裂构造稳定性直接影响该地区工程规划建设。地应力是区域构造稳定性评价的关键性参数, 当前, 关于南迦巴瓦地区地应力场研究成果相对缺乏, 难以满足交通廊道地质安全风险评价实际需求。基于震源机制解数据, 采用应力张量反演方法, 揭示南迦巴瓦地区构造应力场最大主应力方向; 依据断层滑动失稳临界地应力条件, 联合应力形因子和断层摩擦系数反演, 估算南迦巴瓦周边不同区域地应力绝对大小。结果表明: 南迦巴瓦地区现今地应力场最大主应力方向为北东至北北东向; 最大、最小水平主应力大小随深度线性增加梯度分别为0.032~0.0355 MPa/m、0.0227~0.0236 MPa/m, 存在非均匀特征, 估测结果与原位地应力实测值一致性较好; 在当前地应力环境下, 南迦巴瓦周边地区主要活动断裂局部段落存在较大的地震危险性。研究成果可为南迦巴瓦地区工程规划建设提供参考。 

Estimation of in-situ stress field surrounding the Namcha Barwa region and discussion on the tectonic stability

The Namjag Barwa syntaxis is in the eastern Himalayan syntaxis area with the most intensive neotectonic activity. There are many late Quaternary active fault belts and strong seismicities. The tectonic stability of these active fault belts, such as the Jiali, Dongjiu-Milin, and Motuo fault belts, may influence the project's construction. In-situ stress is a critical parameter for estimating regional tectonic stability. Currently, there is a lack of abundant in-situ stress results about the Namjag Barwa syntaxis. It is challenging to assess geological safety risks for major projects. Based on focal mechanism solutions, the paper reveals the orientation of the maximum principal stress surrounding the Namjag Barwa syntaxis using the stress tensor inversion method. According to the critical condition of fault instability, the magnitudes of principal stresses around the Namjag Barwa syntaxis are also estimated by combining the inversion of the stress shape ratio and the frictional coefficient. The results indicate that the maximum principal stress direction in the Namjag Barwa syntaxis area is NE-NNE. The maximum and minimum horizontal principal stresses increase linearly with depth at a gradient of 0.032~0.0355 MPa/m and 0.0227~0.0236 MPa/m, respectively. Heterogeneous features of the in-situ stress field still exist. Generally, the results estimated in this study are in good concordance with the in-situ stress measurements. They can provide reliable in-situ stress parameters for evaluating the tectonic stability in the Namcha Barwa region.