An earthquake of M6½ occurred near Fushan County in the 9th year of Dading Period of the Jin Dynasty(in 1209), which caused a large number of casualties and property losses. Many experts and scholars speculated that the Fushan Fault might be its seismogenic structure, but no in-depth research has been conducted, which greatly hinders the development of earthquake prevention and disaster reduction in the region. The Fushan Fault is located on the east side of the Linfen fault basin in the Shanxi fault depression zone. It is a boundary fault between the Linfen fault basin and the uplift area of the Taihangshan block. Predecessors have done little research on the Fushan Fault. This paper carries out a quantitative study on the late Quaternary activity and displacement rate of the Fushan Fault. First, we carried out remote sensing interpretation, fault surface excavation, collection and testing of fault geomorphological samples in the area of Qianjiao village of Fushan Fault. It is determined that the Fushan Fault starts from Hanzhuang village, Beihan Town in the north, extends to the southwest through Yushipo village, Fenghuangling village, Baozishang village, Zhaojiapo village in Beiwang town, Nanwang village, Zhuge village, Qianjiao village, Guojiapo village, Qiaojiapo village in Tiantan town, Dongguopo village and Zhaishang village in Zhangzhuang town, Lijiatu village and Zhujiashan village in Xiangshuihe town, and terminates in Chejiazhuang village in Xiangshuihe town, with a total length of 24km. The formation age of geomorphological bodies was obtained. It is determined that the latest stratum dislocation event of the fault is later than 7ka, and the fault is a Holocene active fault and has the ability to generate earthquakes of magnitude 7 and above. A total of two phases of stratum dislocation events have occurred on the Fushan Fault since 17ka BP(Late Quaternary): The first-phase event E1 occurred between 17ka and 7ka BP, producing a displacement of 2.04m, the average displacement rate of the Fushan Fault is 0.20mm/a; the second-phase event E2 occurred since 7ka BP, producing a displacement of 3.93m, and the average displacement rate of the Fushan Fault is 0.56mm/a. The displacement rate of the fault has been increasing since the Late Pleistocene. The future seismic hazard of this fault is worthy of attention. This paper also uses land-based LiDAR scanning to obtain the topographic data of the fault plane on the Qiaojiapo village bedrock section of the Fushan Fault(4.5km away from the Qianjiao village section). The isotropic variogram method was used to calculate the fractal dimensions of the fault surface morphology, and the morphological weathering zone was divided, and two phases of ancient seismic events of the Fushan Fault since the Late Quaternary were determined, which are, from old to new, the first-phase event E1 which caused a co-seismic displacement of 3.18m, and the second-phase event E2 which caused a co-seismic displacement of 2.51m. Studies have shown that the bedrock fault plane fractal method is an effective method for studying ancient seismic events in the bedrock area, and its ancient seismic period division is consistent with that of the sedimentary coverage area. Finally, this paper discusses the seismogenic structure of the 1209 Fushan earthquake with magnitude of 6½, and believes that the seismogenic structure of the Fushan earthquake is most likely to be the Fushan Fault. However, due to the lack of a lower age limit and that the only upper limit age is far away from the historical earthquake time, it is necessary to conduct a more detailed investigation and research on the fault to determine whether there can be a revelation of ancient earthquake events with a younger age and comparable magnitude.
This study has greatly improved Fushan County’s risk prevention and control, and territorial planning capabilities.

Based on the 1︰50000 geological and geomorphologic mapping of active fault, the structural geomorphic features and activity of Hancheng Fault are investigated in detail. In the study, we divide the fault into three sections from north to south: the section between Xiweikou and Panhe River, the section between Panhe River and Xingjiabao and the section between Xingjiabao and Yijing, the three sections show different characters of tectonic landform. The section between Xiweikou and Panhe River is a kind of typical basin-mountain landform, where diluvial fans spread widely. In the north of Yumenkou, the fault deforms the diluvial fans, forming scarps, along which the fault extends. In the south of Yumenkou, the fault extends along the rear edge of the diluvial fans. In the section between Panhe River and Xingjiabao the fault extends along the front of the loess mesa. In the section between Xingjiabao and Yijing the fault forms scarp in the loess and extends as an arc shaped zone, and the landform is formed by the accumulative deformation of the fault. The activity of the fault becomes weak gradually from northeast to southwest. The fault activity of the section between Xiweikou and Panhe River is the strongest, and the latest age of activity is Holocene. The slip rate since the mid-Holocene is bigger than 0.8mm/a at Yumenkou. The fault activity of the section between Panhe River and Xingjiabao is weaker than the north part, the fault's latest active age is identified as the later period of Late Pleistocene and the activity becomes weak gradually from northeast to southwest. At the estuary of the Jushui River the slip rate of the fault is about 0.49mm/a since late Late Pleistocene. The fault activity of the section between Xingjiabao and Yijing is the weakest. There is no evidence of paleosol S1 deformed in fault profiles, and only some phenomena of fracture and sand liquefaction in the earlier Late Pleistocene loess. The activity of the fault is in line with the fault landform feature. At macro level, the relationship between the uplifted side and the thrown side of the fault switches gradually from the Ordos uplifting region and the rifted basin to the interior blocks of the rifted basin, which maybe is the regional reason why the activity of the Hancheng Fault becomes weak from the northeast to the southwest.

On the basis of consulting historical records about the positions of Hukou waterfall at different times,we conduct a field geological survey along the Yellow River and ultimately determine the specific locations of the Hukou waterfall in the different periods.Based on this,the retrogressive erosion rates in different periods are calculated as about 1.66m/year during the Xia Dynasty to the Tang Dynasty period,about 1.01m/year in the Tang Dynasty to the Yuan Dynasty,about 0.97m/year in the Yuan Dynasty to the Ming Dynasty,about 1.28m/year in the Ming Dynasty to the Republican period,and 0.6m/year from the Republican period to the present.Considering the complex geological conditions along the Yellow River,the average retrogressive erosion rate of Hukou waterfall on the Yellow River is obtained to be 1.51m/year since the historical records (early Qin Dynasty to the present).Lithology surrounding the Hukou waterfall includes mainly the Triassic gray,gray-green thick-layered mid-grained feldspar sandstone and dark purple,yellow-green mudstone,this hardness and softness combination feature is the unique geological condition of the Yellow River.After abrasing the softer shale driven by water cyclotron at this position,water washes off the debris,causing the overlying feldspar sandstone suspended for a long period.Feldspar greywacke block collapses under accumulative water erosion in long years,and then retrogressive erosion occurs in Hukou waterfall.In the process of 1 ︰ 50 000 active fault mapping of Hancheng Fault,we excavated a trench at Shaojialing,and the trench profile shows that:in the early and middle period of late Pleistocene,there are obvious surface ruptures produced by the fault.Cumulative offset near the trench is more than 20 meters in height difference.Yellow River terraces survey at Yumenkou also confirms that a fault slip of about 20 meters occurred during the early and middle period of the late Pleistocene.Assuming the retrogressive erosion rate is constant,the author thinks the Hancheng Fault was activated at early and middle age of the Late Pleistocene,forming a 20~30m high scarp (knick point),and today's position of Hukou waterfall may be the position of this knick point after the retrogressive erosion of about 40 to 50ka.

Knowledge about regional stress field is a significant basis for better understanding the tectonic activity of faults. This study reports the magnetic fabric investigation performed at sites along the northeastern section of the Hancheng Fault zone after we finished the 1 : 50,000 field mapping of active fualts in this region. Samples were collected at selected sites at Shaojialing, Zhubeizhuang and Shangyukou. Our results show that magnetic fabric, derived from anisotropy of magnetic susceptibility, reveals oblate susceptibility ellipsoids that are slightly modified compared to the inferred original depositional fabric. A dominant distribution of K_max along the NW-SE direction indicates that the northeastern section of the Hancheng Fault zone is subjected to horizontal extensional stress along this direction. A weakly NW-SE directional distribution of K_min is interpreted to reflect the action of horizontal compressive stress. This NW-SE compressive stress at the Shaojialing site appears to be somewhat stronger than that at the Shangyukou and Zhubeizhuang sites. Nevertheless, magnetic fabric properties are located in the oblate area in the P_J-T and Flinn diagrams. This may reflect inhomogeneous distributions of tectonic stresses along the Hancheng Fault zone, indicating that even within a strongly extensional stress-field, prolate magnetic fabric may be difficult to develop. This work may provide basic evidence for further studies on the activity of the Hancheng Fault zone.