天景山断裂带晚第四纪左旋走滑运动速率确定及其空间分布特征

天景山断裂带是青藏高原东北缘一条重要的左旋走滑边界断裂,但是对该断裂左旋走滑运动速率的空间分布特征缺少足够的研究和认识.通过卫星影像解译和野外地质调查,我们在天景山断裂带中段滑动速率限定范围较宽泛的段落选择两个典型的断错地貌观察点,以期获得更为可靠的断裂晚第四纪滑动速率.首先,利用差分GPS和无人机摄影测量技术分别对孟家湾和崾岘沟两点的冲沟或河流阶地的左旋走滑位移量进行精确测量和恢复.然后,利用光释光测年技术对被断错地貌面的年龄进行限定.最后,在综合分析地貌标志物位移和地貌面年龄之间关系以及其形成演化过程,计算和讨论孟家湾和崾岘沟两个点的滑动速率,分别为(1.2±0.3)mm/a和(0.9±0.3)~(1.1±0.2)mm/a.通过与前人研究结果进行对比和分析,认为天景山断裂带晚第四纪左旋走滑运动速率在空间上较为稳定,约为1.1 mm/a.

Determination and Spatial Pattern of the Late Quaternary Left-lateral Slip Rate of the Tianjingshan Fault

The Tianjingshan fault zone is one of the major block-bounding strike-slip faults in northeastern Tibetan Plateau. However, little is known about the spatial pattern of the left-lateral slip rate along the Tianjingshan fault zone. Based on the interpretation of satellite images and field investigation, the authors selected two typical sites in the central segment to constrain the fault slip rate, where the slip-rate ranges are poorly constrained. Firstly, the authors measured and restored the left-lateral offset of streams at Mengjiawan site and fluvial terraces at Yaoxiangou site using differential global positioning system and unmanned-aerial-vehicle photography. Then, the authors dated the ages of the displaced geomorphic surfaces using the optically stimulated luminescence dating method. Finally, the authors calculated and discussed the slip rates at the Mengjiawan and Yaoxiangou sites based on the analysis of the relationship between the offset features and geomorphic surfaces. The derived slip rates of the Mengjiawan and Yaoxiangou sites are (1.2±0.3) mm/a and (0.9±0.3)~(1.1±0.2) mm/a, respectively. Compared with previous results, the authors hold that the Late Quaternary left-lateral slip rate of the Tianjingshan Fault is stable at ~1.1 mm/a.