青藏高原中部崩错断裂晚第四纪滑动速率的精确厘定

The continental escape model and the crustal thickening model are two mainstream models to explain the deformation of the Tibet Plateau. Both of them have estimated the slip rates of large-scale strike-slip fault zones, but the results differ greatly. The former proposed that the Karakorum-Jiali fault zone is the plateau extruded south border with its slip rate of 10-20mm/yr. Due to the lack of quantitative study of the late Quaternary slip rate along Beng Co fault in the fault zone, the understanding of the deformation model of the Tibetan Plateau is restricted. The typical offset geomorphic units were selected using 0.5m worldview satellite imagery and DEM with 1-2m resolution, unmanned aerial vehicle (UAV) aerial photography combined with RTK-GPS measurement of ground control points to obtain high-precision and -resolution DEM data, and the use of LaDiCaoz_v2.1 software automatically extract the best offset and error range, appropriate methods of late Quaternary dating on geomorphic surfaces. We could accurate limitation on late Quaternary slip rate of the Beng Co Fault. The preliminary research has obtained the optimal offsets and dating samples of three sites. The scientific significance is to understand the magnitude of the crustal extrusion and deformation model of the Tibet Plateau, and the response of the Jiali fault zone to the plateau extrusion. The significance of practical needs is to provide basic data for the assessment of fault activity and regional seismic hazard data.

大陆逃逸模型和地壳增厚模型是解释青藏高原变形的两种主流模型，它们都对大型走滑断裂带的滑动速率的进行了估计，结果相差甚大，前者提出喀喇昆仑-嘉黎断裂带作为高原挤出的南部边界带其滑动速率达10-20mm/yr。由于缺少该断裂带崩错段晚第四纪滑动速率的定量研究，制约着对高原变形模型的理解。本项目拟利用0.5m worldview立体像对提取1-2m DEM，对沿线地貌单元进行精细解译，选择典型断错地貌点；开展无人机航拍结合RTK-GPS测量的地面控制点获取高精度、高分辨率DEM，利用LaDiCaoz软件自动提取最佳位错量及误差；选择合适的晚第四纪测年方法，实现精确厘定崩错断裂晚第四纪滑动速率的目标。本项目前期研究已经获得了3个位错地貌点的最佳位错量及测年样品。理解青藏高原地壳物质向东运移规模、理解青藏高原变形模型具有科学意义；为断裂本身的活动习性、区域地震危险性评价提供基础资料。

大陆逃逸模型和地壳增厚模型是解释青藏高原变形的两种主流模型，它们都对大型走滑断裂带的滑动速率的进行了估计，结果相差甚大，前者提出喀喇昆仑-嘉黎断裂带作为高原挤出的南部边界带其滑动速率达10-20mm/yr。由于缺少该断裂带崩错段晚第四纪滑动速率的定量研究，制约着对高原变形模型的理解。利用卫星影像对断层及沿线地貌单元进行了精细解译，选择典型断错地貌点，开展无人机航测获取了高精度高分辨率DEM，利用软件自动提取最佳位错量及误差；对重要地貌面进行了晚第四纪测年；沿着北支断层，位错量分别为4.7±1.1m和 ~8.7±0.7m，对应的年龄为~3.1-3.6ka和3.6-5.2ka；沿着南支断层，位错量为~25±5m，对应的年龄为~9ka，表明右旋走滑崩错断裂全新世滑动速率为4.8±0.5 mm/yr，这与大多数GPS和InSAR数据提取的滑移速率基本一致，略大于古露正断层的伸展速率下限~6±1.8 mm/yr。崩错断裂在全新世期间可能发生过4到5次类似1951年M ≈ 8崩错地震大小的地震，特征滑动量约5 m，复发间隔在1800 -2800 a之间。根据震级/破裂长度经验关系计算，~ 90 km长的地表破裂可能被低估了，这表明该破裂可能至少再延长≈ 20 km，很可能向东南方向，或与1952年Mw ≈ 7.4当雄地震地表破裂重叠。另一方面，崩错断裂的西段似乎至少有1000 a没有发生破裂，这意味着位于该断层西南部的班戈县地区仍面临大地震的风险（Mw ≈ 7.4？）。为理解青藏高原中部构造变形及区域地震危险性提供科学约束。