长岭山北麓断裂晚第四纪活动性及构造稳定性研究

Research on Active Features and Tectonic Stability in the Late Quaternary of the Northern Piedmont Fault of Changlingshan

通过野外调查表明，长岭山北麓断裂晚第四纪以来表现出强烈的新活动性。沿断裂年青冲沟以及最新阶地发生水平左旋位移，通过测量及位移量的分组分析并结合相关年代计算得到，该活动断裂晚更新世以来水平滑动速率为5．1mm／a，垂直滑动速率为0．19mm／a；全新世以来水平滑动速率3．53±0．34mm／a，垂直滑动速率0．29±0．03mm／a。沿断裂全线进行分析并结合断层剖面得到，小红山一带断层上覆0．4～1．2m的坡洪积层（底部TL年龄6．1±0，7kaBP）未被错动，而且Ⅰ级河流阶地及河漫滩相沉积物均未发生变形变位。1927年古浪8．0级地震形成的地表破裂向东抵达下井子沟地区，但未通过陶家山北的明代长城。区域分析表明，长岭山北麓断层构成古浪活动断裂带的东延段，和前人已经确定的天桥沟断层、黄羊川断层一起构成古浪左旋走滑兼逆冲活动断裂带。1927年古浪8．0级地震形成大破裂——贯通型的地震地表破裂带，说明该断裂所在地区为破裂的成熟地段。通过计算，并考虑到古浪大地震的离逝时间以及结合区域资料分析表明，该活动断裂所在地区至少500a内是相对稳定的，1000a的预测时段内发生强、大地震的概率也很低，但是不排除发生中强地震的可能。

According to the geo-seismic field investigation, the northem piedmont fault of Changlingshan has strongly new active features since the late Quatemary. The youngest gullies and the latest terraces along active fault are similar horizontal left-lateral deformation. By the displacement measurement and grouping analysis and interrelated ages, the horizontal slide rate from the late Pleistocene is about 5.1mm/a, and the vertical slide rate is 0. 19mm/a. The horizontal slide rate from the Holocene is about 3.53 ± 0.34mm/a, and also the vertical rate is 0.29 ± 0.03mm/a. With the fault section analysis, about 0.4 - 1.2m slope-flooding sediment（and TL = 6.1 ± 0.7kaBP） covering the active fault have not distorted near the Xiaohongshan area. Therefore, the terrace Ⅰ and fluvial sediment are not deformation and distortion. So, the seismic surface rupture zones generated by the 1927 Gulang earthquake with Ms8.0 is extended eastward Xiajingzigou area at least. But do not pass through the Great Wall （Ming Dynasty） in north of Taojiashan. By regional analysis, the northem piedmont fault of Changlingshan is an eastem segment of the Gulang active fault zone, which is made up of the northem piedmont fault of the Changlingshan, Tianqiaogou active fault and Huangyangchuan active fault which were confirmed in early works. The major rupture-continuous seismic-generated ground ruptures are made by the 1927 Gulang Ms = 8.0 earthquake. So, it is reasonable showing the active fault area is full-blown. According the calculation and considering time-elapsed of the Gulang earthquake, and combining areal datum, the active fault area is relatively stability in 500 years at least, even though in 1000 predicted-year it is a very low probability to happen strong shocks. But the possibility of the mezzo forte earthquake is not excluded.