摘要
2020年1月19日新疆维吾尔自治区伽师县发生M_(S)6.4地震,此次地震为N倾逆冲兼少量走滑型地震,地震的发震构造是南天山柯坪塔格逆冲推覆体最南缘的柯坪断裂,伽师地震的震中位于喀什-伽师流动重力观测网和中国大陆构造环境监测网络GNSS观测网监测区域内。文中选取2015—2021年的流动重力和GNSS观测资料开展分析。采用绝对重力点约束流动重力数据,并进行全网经典平差计算,进而获得重力场变化图像;基于GNSS数据通过GAMIT/GLOBK软件解算获得研究区的运动速率,借助位移与应变的偏导关系获取水平视应变场分布图。之后,分别研究了孕震区的重力场和应变场的变化特征,并综合探讨了孕震区的重力场、GNSS形变场特征与伽师M_(S)6.4地震孕震过程的关系。研究表明:1)一年时间尺度的重力场时变图像较好地反映了伽师M_(S)6.4地震附近区域重力场的系统演化过程,重力变化零等值线拐弯处及“四象限”特征可为地震预报提供有益参考。2)重力场累积变化反映出伽师M_(S)6.4地震前的重力场变化受到区域大断裂的控制,研究区一系列中强震发生在重力翻转变化过程中,重力变化高梯度带特征与地震的发生存在密切关系。根据重力累积变化和时变图像推测此次构造活动可能开始于2018年。3)强震易发生在具有显著重力变化的构造活动断裂带上,2020年伽师6.4级地震发生在重力变化高梯度带拐弯的区域,也是面压缩率变化过渡带地区,区域应变场的增强恢复过程与区域重力场的正、负变化具有一定对应性。
The intracontinental orogeny of Tianshan Mountains has led to strong tectonic activity in the southern Tianshan seismic belt,and strong earthquakes occur frequently at the junction of basins and mountains.On January 19,2020,an M_(S)6.4 earthquake occurred in Jiashi County,Xinjiang Uygur Autonomous Region.This earthquake is of north-dipping thrust motion with a small amount of strikeslip component.The seismogenic structure of the earthquake is the Keping Fault on the southernmost edge of the Keping Tage thrust nappe in the South Tianshan Mountains.The Keping Fault has a total length of about 460km.The overall strike of the fault is near EW,dipping northwest,and the dip angle is more than 45°.It is the boundary fault between Tianshan Mountains and Tarim Basin in Southwest China.The Jiashi M_(S)6.4 earthquake is an important earthquake,which broke the 17 years quiet period of M_(S)6.0 earthquakes since 2003.It is of great value for study on the evolution of regional tectonic deformation.The process of earthquake preparation will be accompanied by changes in geophysical field.Comprehensive analysis of geophysical observation data before and after earthquakes has great practical significance for geodynamics research and identification of earthquake precursor anomaly information.The epicenter of Jiashi earthquake is located in the monitoring area of the“Kashi-Jiashi”mobile gravity observation network and the“Crustal Movement Observation Network of China”GNSS observation.In this paper,the mobile gravity and GNSS observation data from 2015 to 2021 are selected.The mobile gravity observation network uses absolute gravity point constraint to carry out the classical adjustment calculation of the whole network,and then obtains the gravity field change image;The GNSS data are solved by GAMIT/GLOBK software to obtain the movement rate of the study area,and the horizontal apparent strain field distribution is obtained by means of the partial derivative relationship between displacement and strain.By analyzing the dynamic change characteristics of gravity field,velocity field and strain field in the seismogenic area,the relationship between the change of gravity field and GNSS deformation field and the seismogenic process of Jiashi M_(S)6.4 earthquake is comprehensively discussed.The results show that:1)The timevarying images of the gravity field on the time scale of one year better reflect the evolution process of the regional gravity field system near the Jiashi M_(S)6.4 earthquake.The“0”contour of gravity change and its four quadrant characteristics provide useful references for earthquake prediction.2)The cumulative change of gravity field reflects that the change of regional gravity field before the Jiash M_(S)6.4 earthquake was controlled by regional large faults.A series of medium and strong earthquakes in the study area occurred in the process of gravity reverse change.The characteristics of high gradien belt of gravity change are closely related to earthquake occurrence.According to the gravity cumulative change and time-varying image,it is speculated that this tectonic activity may have started in 2018.3)Strong earthquakes are likely to occur on tectonic active fault zones with significant gravity changes.The Keping earthquake of M=6.4 in 2020 occurred in the area where the high gradient zone of gravity changes turns,which is also the transition zone of surface compressibility changes.The variation process of regional strain field corresponds to the positive and negative cumulative changes of the regional gravity field.
作者
朱治国
祝意青
王东振
艾力夏提·玉山
ZHU Zhi-guo;ZHU Yi-qing;WANG Dong-zhen;HUSAN Irxat(Xinjiang Pamir Intracontinental Subduction National Field Observation and Research Station,Urumqi 830011,China;Earthquake Agency of Xinjiang Uygur Autonomous Region,Urumqi 830011,China;Urumqi Institute of Central Asia Earthquake,China Earthquake Administration,Urumqi 830011,China;Second Crust Monitoring and Application Center,China Earthquake Administration,Xi′an 710054,China;Key Laboratory of Earthquake Geodesy,Institute of Seismology,CEA,Wuhan 430071,China)
出处
《地震地质》
EI
CSCD
北大核心
2023年第1期269-285,共17页
Seismology and Geology
基金
新疆维吾尔自治区自然科学基金(2020D01A85)
震情跟踪定向工作任务(2022020505)
新疆维吾尔自治区重点研发专项(2020B03006-2)共同资助。
关键词
伽师地震
重力场变化
GNSS
面应变
构造活动
Jiashi earthquake
variation of gravity field
GNSS
surface strain
tectonic activity
