Dizhi lixue xuebao (Apr 2024)
Late Quaternary surface deformation and tectonic implications of the Bue Co strike-slip fault system in central-western Qiangtang block
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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