characteristics of recent crustal movement in the north section of north-south seismic belt

doi:10.3969/j.issn.0253-4967.2015.04.009

Abstract

Abstract:

Tectonic activity is intense and destructive earthquakes occur frequently in the northern section of the North-South Seismic Belt(NSSB). After the May 12, 2008 Wenchuan earthquake, the North-South Seismic Belt enters a new period of high seismicity. On July 22, 2013, the Minxian-Zhangxian earthquake occurred, which broke the 10-years seismic quiescence of magnitude 6 of the area, indicating an increasing trend of strong earthquakes in the region. Earthquake is the product of crustal movement. Understanding the dynamics of the process of crustal movement may provide basis for earthquake prediction. GPS measurement can provide high-precision, large-scale, quasi-real-time quantitative crustal movement data, that allows us to explore the evolution of crustal movement and its relationship with earthquake, thus providing the basis for determining the seismic situation. Since 2009, the density of mobile GPS measurement stations has significantly improved in the Chinese mainland, and moreover, the Wenchuan earthquake has brought about adjustment of the regional crustal deformation regime. So the introduction of the latest repeat GPS data is important for understanding the features of crustal movement in the northern section of the North-South Seismic Belt. In this paper, we obtained the GPS velocity field, fault profile and baseline time series and analyzed the dynamics of recent crustal movement in the northern section of the North-South Seismic Belt using the 1999a-2014a GPS data of mobile and continuous GPS measurement stations. The results show that: the Qilianshan Fault has a high strain accumulation background. There are locked portions on the Liupanshan Fault, especially in the region of Jingning, Pingling, Dingxi, Longxi. In 2004-2009a, the degree of locking of the Liupanshan Fault got higher. In 2009—2013a, crustal movement on the northern section of the North-South Seismic Belt weakened compared with 1999-2004, 2004-2009, and showed some features as follows: ① The velocity field weakened more markedly near the Qilian-Haiyuan-Liupanshan faults; ②The velocity decreased more significantly in the region north of Qilianshan-Haiyuan Fault than that of the south, resulting in enhanced thrust deformation on the Qilianshan Fault in 2009-2013a and the decreased sinistral shear deformation on the Qilianshan Fault and Haiyuan Fault; ③the velocity field decreased more remarkably at 50km west of Liupanshan Fault, compared to the east region, which led to the locked range on the Liupanshan Fault extending to the range of 100km near the fault zone during 2009-2013 from the previous locked range of 50km near the fault. The GPS baseline time series analysis also reveals a number of structural features in the region: Yinchuan Graben is continuing extending, and the extension in the west is stronger than that in the east. On the southern end of Yinchuan Graben, the deformation is very small.

Key words: north section of North-South Seismic Belt, crustal movement, GPS

摘要：

南北地震带北段构造活动强烈, 强震频发。近年来地震活动有增强的趋势, 震防形势严峻。利用GPS速度场、跨断层速度剖面以及基准站基线时间序列数据, 分析了近年来南北地震带北段地壳运动的动态特征。结果表明, 祁连山断裂具有较高的应变积累; 六盘山断裂存在闭锁, 静宁、平凉、陇西以及定西地区闭锁程度较深; 2004—2009年六盘山断裂闭锁程度加深。2009—2013年与1999—2004年、2004—2009年相比, 南北地震带北段地壳运动减弱, 且呈现出一些特征: 1)祁连山断裂—海原断裂—六盘山断裂附近减弱较显著; 2)祁连山-海原断裂以北区域较以南区域减弱显著, 造成了2009—2013年祁连山断裂挤压逆冲变形增强以及祁连山断裂和海原断裂带左旋剪切变形减弱; 3)六盘山断裂西侧50km以西区域较以东区域减弱显著, 导致六盘山断裂2009—2013年闭锁范围扩大到断裂带附近100km以内, 而此前六盘山断裂的闭锁范围在断裂带附近50km内。GPS基线时间序列分析还显示银川地堑正在持续拉张, 且西部拉张强度强于东部。

关键词: 南北地震带北段, 地壳运动, GPS速度场

CLC Number:

P315.2

WANG Jing, CHAI Chi-zhang, MA He-qing, ZENG Xian-wei, LI Guo-bin. characteristics of recent crustal movement in the north section of north-south seismic belt[J]. SEISMOLOGY AND GEOLOGY, 2015, 37(4): 1043-1054.

王静, 柴炽章, 马禾青, 曾宪伟, 李国斌. 近年来南北地震带北段地壳运动特征[J]. 地震地质, 2015, 37(4): 1043-1054.

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