2022年9月5日四川泸定M_(S)6.8地震深部构造特征  

Deep tectonic pattern of the Luding M_(S)6.8 earthquake on 5th September 2022 in Sichuan Province, China

作　　者：李莹 田建慧 李心怡 李抒予 王琼[1] 高原[1,2,3] LI Ying;TIAN JianHui;LI XinYi;LI ShuYu;WANG Qiong;GAO Yuan(Key Laboratory of Earthquake Prediction,Institute of Earthquake Forecasting,China Earthquake Administration,Beijing 100036,China;School of Earth and Space Sciences,University of Science and Technology of China,Hefei 230026,China;Institute of Geophysics,China Earthquake Administration,Beijing 100081,China)

机构地区：[1]中国地震局地震预测研究所(地震预测重点实验室),北京100036 [2]中国科学技术大学地球和空间科学学院,合肥230026 [3]中国地震局地球物理研究所,北京100081

出　　处：《地球物理学报》2023年第4期1385-1396,共12页Chinese Journal of Geophysics

基　　金：国家自然科学基金项目(42074065和41804046);国家重点研发计划项目(2017YFC1500304);中国地震局地震预测研究所基本科研业务费专项实验室研发计划项目(2021IEF0103和CEAIEF2022010100)共同资助。

摘　　要：2022年9月5日四川省泸定县发生M_(S)6.8地震.本次地震发生在鲜水河断裂南东段端部,位于鲜水河断裂与龙门山断裂、安宁河断裂相交汇的Y形区域.本文利用四川泸定地区的三维S波速度结构,结合地壳厚度、泊松比、GNSS应变场、构造应力场以及各向异性等资料,综合分析了震源区的深部结构.结果显示:泸定M_(S)6.8地震发生在地壳厚度、泊松比、布格重力异常以及最大剪切应变率的快速变化区内;震源附近S波速度在横纵向均表现为高、低速的过渡区域.震源西南侧有一个相对较小的低速体,可能是泸定地震发震的主要深部构造原因.GNSS应变场显示泸定地震位于最大剪切应变率显著高值区.震源机制解显示本次地震震中处于WNW向挤压、ENE向拉张的走滑应力结构,与鲜水河断裂的构造应力场一致.构造应力方向与GNSS主压应变方向有良好的一致性.近场地震记录得到的上地壳S波分裂结果显示,Y形交汇区内快S波主要有两个优势偏振方向,其中WNW(近EW)方向为交汇区的主压应力方向.本文推测,鲜水河断裂是泸定地震的主控断裂,但龙门山断裂对本次地震有重要影响.On 5th September 2022,the M_(S)6.8 earthquake struck Luding county,Sichuan province,China.The earthquake occurred in the southeast end of the Xianshuihe fault(XSHF),which is located in the Y-shaped intersection of the XSHF,the Longmenshan fault(LM_(S)F)and the Anninghe fault(ANHF).Using the data of 3-D S-wave velocity,as well as crustal thickness,Poisson's ratio,GNSS strain,tectonic stress and seismic anisotropy,this paper discusses the deep tectonic pattern of the Luding earthquake.The results show that the epicenter of the Luding M_(S)6.8 earthquake occurred in a special deep tectonic position,with rapid changes in crustal thickness,Poisson's ratio,Bouguer gravity anomaly and the maximum shear strain rates.The S-wave velocity around the hypocenter presents the transition of high and low velocities both horizontally and vertically.A small low-velocity anomaly is located in the southwest side of the epicenter,which may be the main deep tectonic reason for the Luding earthquake.The GNSS strain indicates that the Luding earthquake is in a region with remarkable high maximum shear strain rates.The focal mechanism solutions show that the epicenter is in a strike-slip stress structure of compression WNW and tension ENE,which is consistent with the tectonic stress along the XSHF.The directions of tectonic stress well correspond to those of the GNSS principal compressive strain.The results of upper crustal S-wave splitting obtained from near-field seismic records show two dominant directions of the fast S-wave polarization in the Y-shaped intersection,and the WNW(near EW)orientation is the direction of principal compressive stress.Therefore,this paper presumes that the XSHF is the controlling fault of the Luding earthquake,but the LM_(S)F has a significant effect on this earthquake.

关 键 词：泸定M_(S)6.8地震 S波速度 地壳结构 应力与应变 深部蕴震环境 各向异性 

分 类 号：P315[天文地球—地震学]