山西中条山北麓断裂夏县段新构造运动

通过分析夏县段中条山北麓山麓剥蚀面上的黄土地层，认为山麓剥蚀面形成于2.4 Ma以前。与邻近盆地内钻孔的研究成果对比，得到中条山北麓断裂第四纪以来的垂直活动幅度约700 m，抬升速率为0.29 mm/a。GPS测量得到断层将末次冰期极盛期形成的冲沟阶地垂直错断7 m，垂直活动速率为0.28~0.5 mm/a。探槽揭示，距今2 万年以来断层有四次活动--距今8000 年之前、距今4100 年前后、距今3100 年和距今720 年以后。断距分别为大于2m、0.6m、1.55 m和0.25 m。断层活动速率为0.22~0.55 m/a。

Neotectonic activity in Xiaxian segment of the North Zhongtiao Mountain Fault Zone,Shanxi

North Zhongtiao Mountain Fault Zone (NZFZ) is the east and south boundary fault of Yuncheng Basin, which is the southernmost basin of Shanxi Graben System. NZFZ comprises three segments, i.e. the western (Hanyang) segment, the middle (Xiezhou) segment and the eastern (Xiaxian) segment. This paper focuses on the Xiaxian segment of NZFZ. We characterize the pattern of this segment on the basis of the analysis on loess sediments, drilling results and GPS data. The loess/paleosol sequence constrains chronologically the formation of the paleo-piedmont developing in the northwest front of the east part of the Zhongtiao Mountains at about 2.4 MaBP. Based on the drilling results from the adjacent Yuncheng Basin, we define that the total vertical displacement during the Quaternary is about 700 m, which gives rise to an uplift rate of 0.29 mm/a. In response to uplifting of the Zhongtiao Mountain, several terraces were formed along the gullies flowing through the fault. The formation age of the deformed terrace T2 is dated at about 2.5 kaBP by 14C dating method. Together with the deformation of ~7 m according to the field investigation and GPS measurements, the slip rate is defined as 0.28-0.29 mm/a. At the Xiaxian segment, four paleoseismic events were revealed by the trenching study at Xiayandi. The oldest event was constrained at 20-6 kaBP with the vertical displacement of >2 m. The subsequent event occurred around 4140 ± 30 aBP with a vertical displacement of 0.6 m. The third event occurred at 3100 aBP with a vertical displacement of 1.55 m. The youngest event is constrained chronologically at 720 aBP with a vertical displacement of 0.25 m. Based on the total displacement of >4.4 m, we conclude that the vertical slip rate should be 0.22-0.55 mm/ a. The above results on NZFZ are different from the previous studies, which propose a relatively inactive tectonic setting during Holocene in the present study area.