Late Quaternary surface deformation and tectonic implications of the Bue Co strike-slip fault system in central-western Qiangtang block
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摘要:
班公-怒江缝合带(班怒带)是青藏高原内部羌塘地块与拉萨地块之间的重要边界，研究该边界带上共轭走滑断裂第四纪晚期的几何结构与变形特性对于理解高原内部在印度-欧亚板块碰撞作用下形成的空间差异响应和构造模型具有重要意义。位于班怒带西段的布木错断裂系包括北东向布木错断裂和北西向纳屋错断裂，通过遥感解译和野外地质调查，明确了这两条断裂在第四纪晚期的构造特征和最新的地表变形特征。结果显示，两条断裂自第四纪晚期以来的活动特征明显，并且近期都经历过一次大地震，产生了地表破裂。据此推测班怒带西段北西、北东两组断裂的最新活动强度接近，羌塘地块南部边界现今变形可能受控于两组断裂的共同影响，并已延伸至块体内部。以上发现进一步证明，青藏高原内部物质受中—下地壳流的驱动作用，通过走滑断层和正断层持续向北扩展。
Abstract:Objective The Bangong-Nujiang Suture Zone (BNSZ) serves as a boundary between the Qiangtang and Lhasa terranes of the Tibetan Plateau. The geometric structure and deformation characteristics of the "V" -shaped conjugate strike-slip faults along this late Quaternary boundary are important for understanding the spatially variable responses and tectonic models formed within the plateau as a result of the India-Eurasia plate collision. However, previous studies have primarily focused on the kinematic properties and activity rates of strike-slip faults in the eastern segment of the suture zone. The scarcity of information on the activity characteristics of strike-slip faults and paleoseismic events in the western segment of the suture zone has hindered our understanding of regional tectonic deformation and seismic activity. The Bue Co fault system, located in the western section of the BNSZ, is a (conjugate) strike-slip fault system consisting of the NE-trending Bue Co and NW-trending Lamu Co faults.
Methods This study employs a combination of remote sensing interpretation and field surveys, utilizing high-resolution Digital Surface Models (DSM) collected by unmanned aerial vehicles (UAV) to conduct a detailed analysis of surface ruptures and systematically decipher the geometric morphologies and late Quaternary deformation evidence of the NE-trending Bue Co Fault and the NW-trending Lamu Co Fault in the western section of the BNSZ.
Results This study revealed significant fault activity since the late Quaternary period, with evidence of recent large earthquakes that caused surface ruptures extending >60 km along both faults. The Bue Co fault exhibits left-lateral strike-slip, with recent seismic displacements ranging from 3.7 to 4.2 m, whereas the Lamu Co fault shows right-lateral strike-slip with minimum displacements of 2.7 m. Both faults display normal faulting components in their surface rupture zones, and the vertical displacements are cumulative across landforms of various ages, indicating long-term fault activity. The latest activity intensities of the NW and NE faults in the western BNSZ were similar, suggesting that the deformation of the southern boundary of the Qiangtang block may be controlled by both fault sets, which extend into the interior of the block.
Conclusion These findings reveal that (1) both the Bue Co and Lamu Co faults can generate strong earthquakes of magnitude ≥7, indicating active tectonic deformation and a high seismic hazard potential in the western section of the BNSZ; (2) the deformation in the western BNSZ is concentrated along the NW-trending strike-slip faults and active along the NE-trending strike-slip faults, which may jointly control the southern boundary of the eastward extrusion of the Qiangtang terrane and have extended into the interior of the terrane; and (3) the continuous deformation pattern is supported, revealing that material within the Tibetan Plateau is driven by mid-lower crustal flow extruding eastward, with the southern boundary of the extrusion potentially continuing northward through a series of strike-slip and normal faults.
Significance These conclusions deepen our understanding of the activity and seismic potential of strike-slip faults in the western BNSZ and provide novel insights into the internal tectonic deformation patterns and dynamic background of the Tibetan Plateau. Furthermore, this study provides an essential theoretical foundation for regional stability assessments and disaster mitigation planning.
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表 1 布木错断裂系位移量分布表
Table 1. Statistic table of displacement in the Bue Co fault system
断裂名称 经度 纬度 断错标志 位移量/m 误差/m 布木错断裂 81°29′55.14″ 33°15′50.10″ 冲沟左旋 11.0 0.5 81°29′52.02″ 33°15′40.44″ 冲沟左旋 3.7 0.2 81°29′35.71″ 33°14′59.25″ 沟壁左旋 43.0 3.0 81°29′51.82″ 33°15′40.52″ 小沟左旋 4.2 0.3 81°29′54.82″ 33°15′50.25″ 小沟左旋 4.5 0.4 81°29′54.58″ 33°15′50.25″ 小沟左旋 6.4 0.6 纳屋错断裂 81°43′41.52″ 33°13′16.02″ 深沟右旋 7.3 1.2 81°43′31.62″ 33°13′20.10″ 小溪右旋 4.5 0.5 81°43′32.78″ 33°13′19.41″ 小溪右旋 2.7 0.3 81°43′33.49″ 33°13′19.10″ 冲沟右旋 13.7 1.1 81°43′40.51″ 33°13′16.28″ 小溪右旋 8.3 2.0 81°43′41.61″ 33°13′15.70″ 沟壁右旋 10.3 2.4 81°43′44.41″ 33°13′14.21″ 沟壁右旋 27.0 3.0 81°43′45.32″ 33°13′13.85″ 沟壁右旋 15.0 1.5 81°43′45.66″ 33°13′13.58″ 深沟右旋 14.0 1.5 
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