Slip rate is an important parameter for the quantitative study of active fault and can be used to reflect the mode and intensity of fault activity. However, the selection of geomorphic surface, the acquisition of displacements, and the limitation of chronologic methods result in challenges to constrain the slip rate. A series of boreholes and geochronology studies revealed a continuous sedimentary sequence of the Quaternary in the Yuncheng Basin in the southern Shanxi Graben System. Multiple late Quaternary river terraces have developed and been preserved in the northern piedmont of the Zhongtiao Shan. The activities of the north Zhongtiao Shan Fault resulted in the elevation difference between the strata in the Yuncheng Basin and the river terraces. In this study, we chose the geomorphic units of the Xiaolicun River and combined them with the results of boreholes in the Yuncheng Basin to constrain the slip rates of the north Zhongtiao Shan Fault since the Late Pleistocene. Based on field observation and remote sensing image interpretation, we established the distribution and sedimentary characteristics of four terraces and the latest alluvial fan of the Xiaolicun River. Two main faults(F₁ and F₂)and a series of fractures or branch faults have been identified in these sedimentary strata. The high-resolution DEM of the faulted landform of the Xiaolicun River was obtained using UAV photogrammetry technology. Combined with a stratigraphic outcrop survey, the landform and sedimentary section across the fault were constructed. The abandonment ages of the terraces T₄, T₃, T₂, and T₁ have been determined as(214.3±13.9)ka, (118.5±6.4)ka, (59.6±2.4)ka, and(10.9±0.5)ka by OSL dating, respectively. The chronological results of the AMS ¹⁴C dating show that the alluvial fan north of F₂ was deposited at 35~1ka. Based on these results, this study established the relationship between the geomorphic evolution of the Xiaolicun River and the activities of the north Zhongtiao Shan Fault. Since the late Middle Pleistocene, F₁ had been active, accompanied by the abandonment of the T₄. At~120ka, the terrace T₃ was formed, F₁ was no longer active, but F₂ began to be active and raise T₃ and T₄ in the footwall. Since then, the Xiaolicun River has undergone rapid incision and formed T₂ and T₁. The continuous activities of F₂ maintained T₄-T₁ in an uplifted state and formed a series of fractures in the alluvial fan. Based on this evolutionary relationship, T₄, T₃ and their corresponding strata in the boreholes of the Yuncheng Basin were used to constrain the slip rate of the north Zhongtiao Shan Fault in this study. After determining the depth in boreholes corresponding to the abandoned ages of T₄ and T₃, subtracting the influence of the surface slope and the activities of the southern Salty Lake Fault, and considering the depth error caused by climate change, the vertical displacements of the north Zhongtiao Shan Fault since the two periods were obtained with the vertical slip rate of(0.31±0.05)mm/a and(0.34±0.04)mm/a, respectively. Our results indicate that the slip rates of the north Zhongtiao Shan Fault since the late Middle Pleistocene are greater than those since the Late Pliocene and Quaternary.

The Qilianshan north-edge thrust (QNT)is located at the boundary between the northern margin of the Qilianshan mountain and Hexi Corridor, with a length over 700km. The Minle-Damaying fault (MDF), trending NWW, is part of the eastern section of the QNT, cutting through the Minle and Wuwei Basins. Hexi Corridor is a region of intense seismic activities, where many large earthquakes have been documented in history, such as the M7.5 Gaotai earthquake in 180, M8.5 Haiyuan earthquake in 1920, M8.0 Gulang earthquake in 1927 and the M7.6 Changma earthquake in 1932. While, there is no seismic record on the MDF. The Dongda River flows across the MDF from south to north. One of the tributary of the Dongda River, Xie River, has very well preserved terraces (T₆-T₁)which were offset by the MDF. On these terraces, there is clear trace of scarps, of which the height increases from terraces T₃ to T₆, indicating an accumulation of offset with time. In order to acquire the cross-section of scarps, unmanned aerial vehicle (UAV)scanning was implemented. With a digital camera mounted on, the UAV scanned an area of 0.52km² and digital elevation model (DEM)was generated with an accuracy of 0.2m vertically. The Thompson's method was utilized to conduct linear regressions on both the hanging wall and foot wall of the fault. The difference between the intercepts of the regression lines with the vertical line going through the intersection of the scarp surface on the fault surface is considered as the vertical offset. Terraces from T₆ to T₃ are very well preserved where MFD intercepts the Xie river, while T₂ and T₁ are badly eroded at the same location. Utilizing the cross-sections extracted from high resolution DEM, we estimate that the vertical offsets of T₆-T₃ are 13.26~15.67m, 9.74~10.13m, 5.86~7.35m and 5.03~5.60m, respectively, with 95%confidence interval. From the offsets of terraces, at least 4 paleo-seismic events are indentified. Terraces were dated by the AMS ¹⁴ C dating, yielding ages (cal BP)of T₆-T₂ as (16 405±210)a, (111 975±21)a, (5 697.5±210)a, (4 470.5±54.5)a and (3 137.5±77.5)a. Liner regression was performed for the relation between the ages and the offsets of terraces, resulting in the average vertical slip rate of MDF since the formation of T₆ as 0.91 average v. As the dip of MDF is about 35°, the shortening rate is estimated to be (1.3±0.13)mm/a. This study provides important parameters for the analysis of seismic activity in heavily populated Minle and Yongchang areas.

Shanxi Graben System(SGS)is a NNE-trending tectonic system located in the eastern and southern edges of Ordos Block and between Yinshan tectonic zone and Qinling tectonic zone. Composited with a series of NNE-, NE-trending graben basins, SGS is an important seismic zone in North China. Yuncheng Basin locates in the southern end of SGS, and is the deepest basin of the system. It is a half-graben with a shallow northern part and a deep southern part. As the south and east boundary of Yuncheng Basin, the North Zhongtiaoshan Fault Zone(NZFZ)played a key role in the development of the topology and tectonics setting of Yuncheng Basin. NZFZ is a normal fault zone, NE- to NEE-trending and 130km long. This fault zone can be divided into 3 segments: the south, the middle, and the north segment, and there are no historical M≥7, but only 3 M=6 have taken place. Previous study suggests that the tectonic activity in this area is low and the earthquake interval is relatively long; seismic activity in the north and south segments is the weakest: the earthquake recurrence interval in the north segment is >50ka and it has not been active for >50ka, the interval of the south segment is ～12ka and its last movement is about 7ka ago. Our work tells a different story: based on thorough fieldwork, satellite imagery analysis, and trench investigation, we found that there have been multiple earthquake events taking place in all of the 3 segments during Holocene. This study includes two trenches that locate in the south and middle segments of NZFZ, each of them renders 3 paleo-earthquake events: a 10 570～8 010a BP event, an around 6 670～6 550a BP event, and a 2 110～320a BP event in TC-1; a 7 930～11 300a BP event, a 4 800～6 010a BP event, and a 2 680a BP event in TC-2. Through comparing these events with other 2 trenches in the middle segment of NZFZ(a XTC trench that renders a 19 980a BP event and a 8 570～7 780a BP event with >2.2m vertical displacement; a XLC trench that renders a 8 980～7 340a BP event with ～1.8m vertical displacement), we identified: a 8 570～8 010a BP event which broke through both middle and south segment of NZFZ with a largest known vertical displacement of >2.2m and 95km surface rupture, a 4 800～6 010a BP and a 2 110～320a BP event with 7～30km surface ruptures and largest known vertical displacements of 0.7m and 1.2m, respectively. The recurrence interval of these events is about 3 500a. Calculated with empirical formula of normal fault in North China, the magnitude of the 8 570～8 010a BP earthquake should be at least 8.0, and the magnitudes of the 4 800～6 010a BP and 2 110～320a BP events are both ≈7.0. These findings suggest that, as a Holocene active fault zone which made up with multiple faults, the middle and south segments of NZFZ have shown strong seismic activity and have triggered multiple earthquake events during the Holocene. Contrary to previous study, the activity of south segment might not be the weakest, and it is possible that the south segment is more seismic active than the middle segment.