STUDY ON THE RECENT DEFORMATION CHARACTERISTIC AND STRUCTURAL DEFORMATION MODEL OF THE SOUTH-EASTERN MARGIN OF ORDOS BLOCK

doi:10.3969/j.issn.0253-4967.2021.03.005

Abstract

Abstract: The southeastern margin of the Ordos block is a key area for dynamic transformation from collision and compression in the western part of the Chinese mainland to extension in the east, and also is the junction of the NE-SW trending structure in the north and near the E-W trending structure in the south of the North China block. The tectonic activity in the southeastern margin of the Ordos block is intense. In this region, the Houma-Yuncheng section is a noteworthy area for medium- and long-term large earthquake risk determined by China Earthquake Administration, which involves three tectonic units: Linfen Basin, Yuncheng Basin and Emei Platform. The potential seismogenic faults include the Hancheng Fault, the southern margin fault of Emei Platform and the piedmont fault of Zhongtiao Mountains. Because the neotectonic movement in this region is mainly dominated by strong differential movement, it is important to estimate the fault kinematics parameters based on the high-resolution vertical crustal movement observation constraints.
Fault locking depth and slip rate are important indicators to judge the risk of future earthquakes. When the accumulation time of fault seismic moment and fault length are given, the larger fault locking depth and higher slip rate will cause the greater energy accumulation and stronger future earthquakes risk of the fault. Based on the traditional leveling and GPS data, previous studies found that the southeastern margin of the Ordos block is perhaps experiencing strong tectonic movement. However, the measuring point density of the above technical means is difficult to satisfy the quantitative study of the current activity characteristics of specific faults. Therefore, the interferogram stacking technique is used to obtain the spatial high-resolution InSAR average deformation rate field of the study area based on the Radarsat -2 wide-mode image in this paper firstly. At the same time, the three-component velocity of GPS continuous station in the study area is projected into the radar line of sight direction. After unifying the reference datum, comparative analysis was conducted to evaluate the accuracy and reliability of InSAR results. The results show that the standard deviation of the difference between the short-term InSAR and the long-term GPS observation values is 2.7mm. The annual crustal deformation field obtained by using the interferogram stacking technology in the study area has a high accuracy, which can reflect the characteristics of regional crustal movement. It also indicates that the regional crustal short-term deformation is consistent with the long-term deformation. Secondly, the dip-slip fault dislocation model and particle swarm optimization(PSO)were used to invert the main fault slip rate and locking depth, the inversion was repeated 1 000 times, and the optimum estimate of parameters was obtained by statistical analysis of results and uncertainty. The fault slip rate and locking depth data approximately obey the normal distribution, and the stability is good; the dip angles of faults are skewed but concentrated. The above results show that the fault movement parameters obtained from InSAR deformation field inversion are reliable and can be used for regional tectonic movement analysis. Finally, based on the data of regional geological structure, fault slip rate, fault locking depth and present seismic activity, this paper analyzes the variation characteristics of InSAR deformation field, and discusses the fault tectonic movement mode, future seismic risk and regional tectonic deformation pattern in the southeastern margin of Ordos. The results show that the tectonic and nontectonic deformations are superimposed on the southeastern margin of Ordos. Tectonic deformation mainly occurs near active faults, which is related to fault slip rate and closure depth. Nontectonic deformation mainly occurs in the Quaternary strata inside the basin, which is related to the thickness of the aquifer and the amount of groundwater extraction, and the maximum can reach 5cm/a. The slip rate of the fault at the northern foot of the Zhongtiao Mountains and the northern margin of the Emei Platform is 0.37mm/a and 0.74mm/a, and the blocking depth is 3.4km and 4.3km, which are relatively shallow. It may indicate that the fault was not completely closed after the last strong earthquake and is dominated by shallow seismic activity. The slip rate of the fault on the southern margin of the Emei Platform is 0.47mm/a, and the closure depth is 0.95km, indicating that the faults are mainly creepy. The counterclockwise rotation of the Ordos block and the eastward extrusion and escape of the Qinling Mountains formed a quasi-triple junction structural area on the southeastern margin of Ordos, characterized by strike-slip-extension transition.

Key words: southeastern margin of Ordos block, InSAR, GPS, slip rate, locking depth, tectonic deformation model

摘要： 鄂尔多斯块体东南缘是中国大陆西部碰撞挤压到东部伸展拉张动力学转换的关键地区, 其新构造运动以强烈的差异升降运动为主, 在该区开展空间高分辨率的地壳垂直运动观测尤为重要。文中基于Radarsat-2宽模式影像, 采用干涉图堆叠(Stacking)技术获得了研究区的空间高分辨LOS向平均形变速率场, 并与研究区域内长期观测的GPS连续站数据开展对比分析。在此基础上, 利用倾滑断层位错模型、粒子群算法(PSO)反演了主要断裂的滑动速率和闭锁深度, 结果表明: 1)利用干涉图堆叠(Stacking)技术得到的研究区年尺度地壳形变场具有较高的精度, 且区域地壳短期形变与长期形变具有一致性。 2)鄂尔多斯东南缘的构造和非构造形变相互叠加, 构造形变主要发生在活动断裂附近, 与断层滑动速率和闭锁深度有关。非构造形变主要发生在盆地内部的第四纪地层, 与含水层厚度和地下水开采量有关, 最大量级>5cm/a。 3)中条山北麓断裂和峨嵋台地北缘断裂的滑动速率为0.37mm/a和0.74mm/a, 闭锁深度为3.4km和4.3km, 可能表明断裂在最后一次强震发生后还未完全闭锁, 现今以浅部活动为主。峨嵋台地南缘断裂的滑动速率为0.47mm/a, 闭锁深度为0.95km, 表明断层现今可能以蠕滑活动为主。 4)鄂尔多斯地块的逆时针旋转和秦岭山地的向E挤出逃逸, 形成了鄂尔多斯东南缘以走滑-伸展转换为特征的似三联点构造区。

关键词: 鄂尔多斯东南缘, InSAR, GPS, 滑动速率, 闭锁深度, 构造变形模型

CLC Number:

P315.2

LIU Rui-chun, ZHANG Jin, GUO Wen-feng, CHEN Hui, ZHENG Ya-di, CHENG Cheng. STUDY ON THE RECENT DEFORMATION CHARACTERISTIC AND STRUCTURAL DEFORMATION MODEL OF THE SOUTH-EASTERN MARGIN OF ORDOS BLOCK[J]. SEISMOLOGY AND GEOLOGY, 2021, 43(3): 540-558.

刘瑞春, 张锦, 郭文峰, 陈慧, 郑亚迪, 成诚. 鄂尔多斯块体东南缘现今的变形特征与构造模式探讨[J]. 地震地质, 2021, 43(3): 540-558.

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