Abstract: Located at the bend of the northeastern margin of Qinghai-Tibet Plateau, the Haiyuan fault zone is a boundary fault of the stable Alashan block, the stable Ordos block and the active Tibet block, and is the most significant fault zone for the tectonic deformation and strong earthquake activity. In 1920, a M8.5 earthquake occurred in the eastern segment of the fault, causing a surface rupture zone of about 240km. After that, the segment has been in a state of calmness in seismic activity, and no destructive earthquakes of magnitude 6 or above have occurred. Determining the current activity of the Haiyuan fault zone is very important and necessary for the analysis and assessment of its future seismic hazard.
To study activity of the Haiyuan fault zone, the degree of fault coupling and the future seismic hazard, domestic and foreign scholars have carried out a lot of research using geology methods and GPS geodetic techniques, but these methods have certain limitations. The geology method is a traditional classical method of fault activity research, but dislocation measurement can only be performed on a local good fault outcrop. There are a limited number of field measurement points and the observation results are not equally limited depending on the sampling location and sampling method. The distribution of GPS stations is sparse, especially in the near-fault area, there is almost no GPS data. Therefore, the spatial resolution of the deformation field features obtained by GPS is low, and there are certain limitations in the kinematic parameter inversion using this method.
In this study, we obtain the average InSAR line-of-sight deformation field from the Maomaoshan section to the mid-1920s earthquake rupture segment of the Haiyuan earthquake in the period from 2003 to 2010 based on the PSInSAR technique. The results show that there are obvious differences between the slip rates of the two walls of the fault in the north and the south, which are consistent with the motion characteristics of left-lateral strike-slip in the Haiyuan fault zone. Through the analysis of the high-density cross-fault deformation rate profile of the Laohushan segment, it is determined that the creep length is about 19km. Based on the two-dimensional arctangent model, the fault depth and deep slip rate of different locations in the Haiyuan fault zone are obtained. The results show that the slip rate and the locking depth of the LHS segment change significantly from west to east, and the slip rate decreases from west to east, decreasing from 7.6mm/a in the west to 4.5mm/a in the easternmost. The western part of the LHS segment and the middle part are in a locked state. The western part has a locking depth of 4.2~4.4km, and the middle part has a deeper locking depth of 6.9km, while the eastern part is less than 1km, that is, the shallow surface is creeping, and the creep rate is 4.5~4.8mm/a. On the whole, the 1920 earthquake's rupture segment of the Haiyuan fault zone is in a locked state, and both the slip rate and the locking depth are gradually increased from west to east. The slip rate is increased from 3.2mm/a in the western segment to 5.4mm/a in the eastern segment, and the locking depth is increased from 4.8km in the western segment to 7.5km in the eastern segment. The results of this study refine the understanding of the slip rate and the locking depth of the different segments of the Haiyuan fault zone, and provide reference information for the investigation of the strain accumulation state and regional seismic hazard assessment of different sections of the fault zone.

Key words: Haiyuan fault zone, time series InSAR, fault locking degree, slip rate

摘要： 文中利用2003—2010年2个轨道上的Envisat ASAR长条带雷达数据，采用PSInSAR时序处理方法，获取了海原断裂带毛毛山—老虎山段及狭义海原断层段（1920年8.5级地震破裂带）的InSAR视线向平均形变速率场，发现南、北2盘的形变速率场存在明显差异，与海原断裂带左旋走滑的运动特征相符。通过对老虎山段进行高密度跨断层形变速率剖面分析，确定老虎山段的蠕滑长度约19km。基于二维反正切模型对InSAR形变剖面进行了拟合，获得了海原断裂带不同位置的断层闭锁深度及深部滑动速率。结果表明，老虎山段的滑动速率自西向东逐渐减小，由西段的7.6mm/a减小至最东端的4.5mm/a；老虎山西段与中段处于闭锁状态，西段的闭锁深度为4.2～4.4km，中段的闭锁深度为6.9km，而老虎山东段的闭锁深度1km，即浅地表存在蠕滑现象，蠕滑速率为4.5～4.8mm/a。1920年海原断裂带破裂段整体处于闭锁状态，滑动速率与闭锁深度自西向东均逐渐增加，滑动速率由西段的3.2mm/a增加至东段的5.4mm/a，闭锁深度由西段的4.8km增加到东段的7.5km。文中的研究结果细化了对海原断裂带不同段的滑动速率和闭锁深度的认识，并为探讨断裂带不同段的应变积累状态及区域地震危险性评估提供参考信息。

关键词: 海原断裂带, 时序InSAR, 断层闭锁深度, 滑动速率