Abstract:

The Xiaojiang fault zone is the southernmost branch fault of the Xianshuihe-Xiaojiang left-lateral strike-slip fault system, together with the Xianshuihe Fault, the Anninghe Fault and the Zemuhe Fault, which forms the eastern boundary of the Sichuan-Yunnan block on the southeast margin of Qinghai-Xizang Plateau and plays an important role in accommodating the clockwise rotation around the eastern Himalayan syntaxis and S-SE extrusion of the Sichuan-Yunnan block. The scientific understanding of geometric structures, the slip rate, the strong earthquake recurrence and the mechanism of deformation compatibility of different segments of the Xiaojiang fault zone, especially the intersection with the Red River fault zone, remains highly debated. In order to better understand the role of the Xiaojiang fault zone in the process of material extrusion of the southeastern margin of the Qinghai-Xizang Plateau, based on the systematic summary of previous research results about the Xiaojiang fault zone, topographic relief and slope in the study area were extracted, and combined with geomorphological characteristics analysis, the geometric structure and kinematic characteristics, strike-slip rate at different time scales, seismic activity and deformation coordination with the Red River fault zone of the Xiaojiang fault zone are combed and summarized. combined with geomorphological characteristics analysis by extracting the relief and slope of the study area. The geometric segments and the late Quaternary activity characteristics of each segment of the Xiaojiang fault zone are described in detail. Then, we mainly reviewed the slip-rates at different timescales(geodetic scale, late Quaternary scale, and long time scale) of the Xiaojiang fault zone and their spatio-temporal variations. The seismicity characteristics of the Xiaojiang fault zone are summarized from three aspects: Paleoearthquakes, historical earthquakes and present earthquakes. The geometric relationship, deformation decomposition and transformation of faults at the intersection of the Xiaojiang fault zone and the Red River fault zone are analyzed. Besides, the geometric and kinematic characteristics of the deformation of the Xiaojiang fault zone and the coupling relationship between deep and shallow tectonic deformation are discussed, combined with geomorphic feature analysis. At last, he risk of future strong earthquakes in the Xiaojiang fault zone is discussed based on the results of previous studies on heterogeneous interseismic coupling along the Xiaojiang fault zone, etc. Through comprehensive analysis, it is concluded that the geometric and kinematic characteristics of the Xiaojiang fault zone are consistent with a clockwise rotation of the Sichuan-Yunnan block about the eastern Himalayan syntaxis. The deep tectonic process has an obvious controlling effect on the shallow tectonic deformation, and the Xiaojiang fault zone has a profound influence on the crustal structure, the deformation of the medium and the process of material migration. As the southeast boundary fault of the Sichuan-Yunnan block, the Xiaojiang fault zone has well restricted the S-SE movement of crustal material during the process of extrusion from the southeast margin of the Qinghai-Xizang Plateau to the east. The results show that the strike adjustment of the Xiaojiang fault zone, the change of movement characteristics, the spatio-temporal evolution of strike-slip rate, the segmentation of geomorphic parameters and the distribution of seismic activity are highly consistent with the clockwise rotation direction of the Sichuan-Yunnan block around the eastern Himalayan syntaxis. There is an obvious coupling relationship between deep tectonic action and shallow tectonic deformation in the Xiaojiang fault zone. The risk of strong earthquakes is high in the Xiaojiang fault zone, especially in the Qiaojia-Dongchuan area in the north and the confluence area of the Red River fault zone in the south. The probability of strong earthquakes in the future is increasing in each section of the Xiaojiang fault zone, especially in the northern section of the Qiaojia-Dongchuan fault zone and the intersection of the Red River fault zone and the Xiaojiang fault zone, the risk of strong earthquakes in the future is high, which should be paid great attention to.

Key words: The Xiaojiang fault zone, strike-slip rate, deformation compatibility, earthquake activity, hazard of strong earthquake

摘要：

小江断裂带是川滇块体东边界的南段主干断裂, 在川滇块体围绕喜马拉雅东构造结顺时针旋转并侧向挤出过程中起调节作用。为了更好地理解小江断裂带在青藏高原物质向E挤出过程中扮演的角色, 文中在系统总结前人研究成果的基础上, 梳理其几何结构、 不同时间尺度走滑速率、 地震活动特征、 与红河断裂带的变形协调等, 结合地貌特征分析, 重点讨论了变形几何学与运动学特征及深浅构造变形之间的关系和未来强震危险性。结果表明, 小江断裂带走向调整、 走滑速率和运动性质沿走向的变化与川滇块体绕喜马拉雅东构造结顺时针旋转一致; 深部构造作用与浅部构造变形具有明显的耦合关系。小江断裂带各段现今的强震危险性均较高, 特别是北段巧家—东川地区和南段与红河断裂带交会的地区, 应予以高度重视。

关键词: 小江断裂带, 滑动速率, 变形协调, 地震活动, 强震危险性