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.

Based on ANSYS parallel software platform, and according to active tectonic block region division and distribution of active faults in North China, and combined with GPS data, the range of the numerical model is defined as 99.8°～121.4°E, 27.9°～42.3°N, which contains a majority of the North China active tectonic block region and parts of other block regions including the Tibetan plateau, the Xiyu, South China, and the Northeastern Asia. The model is divided into 416582 elements whose average side length is 25km with 582392 nodes. The main research results are: (1)Simulation of crustal movement velocity and analysis. The results show that the velocity of crustal movement in North China as a whole decreases from east to west and increases from north to south. It is an almost match between simulation results and GPS observed velocity field. (2)Simulation of the slip of faults and analysis. Considering all known late Quaternary active faults in North China in the model and according to the simulation results, the slip of faults obtained from simulation and that from geological survey are almost consistent. (3)Simulation of strain fields and analysis. By numerical simulation, the minimum strain and the maximum principal strain in North China in 1999-2004 and 2004-2007 are calculated. The horizontal strain direction in North China is in accord with the strain direction obtained from inversion of focal mechanism solutions, GPS observations, etc. by previous studies.