2022年四川芦山MS6.1地震前应力状态研究
张致伟1,2,曾宪伟3,王迪1,路茜1,王玮铭1,杨鹏1,龙锋1

(1.四川省地震局,四川 成都 610041; 2.成都理工大学,四川 成都 610059; 3.宁夏回族自治区地震局,宁夏 银川 750001)

芦山MS6.1地震; 芦山MS7.0地震; 震源机制解; 应力张量方差; b值; 应力状态

Study on the Stress State before the 2022,Lushan,Sichuan MS6.1 Earthquake
ZHANG Zhiwei1,2,ZENG Xianwei3,WANG Di1,LU Qian1,WANG Weiming1,YANG Peng1,LONG Feng1

(1.Sichuan Earthquake Agency,Chengdu 610041,Sichuan,China)(2.College of Geophysics,Chengdu University of Technology,Chengdu 610059,Sichuan,China)(3.Earthquake Agency of Ningxia Hui Autonomous Region,Yinchuan 750001,Ningxia,China)

the Lushan MS6.1 earthquake; the Lushan MS7.0 earthquake; focal mechanism solution; stress tensor variance; b value; stress state

DOI: 10.20015/j.cnki.ISSN1000-0666.2024.0061

备注

为研究2022年6月1日四川芦山MS6.1地震的孕育和发生过程,采用CAP方法反演了2013年芦山MS7.0主震及MS≥5.0余震的震源机制解,并基于应力张量方差与b值时空分布特征,探讨了芦山MS6.1地震的力学机制和震源区的应力状态。结果表明:2022年芦山MS6.1地震震源机制表现出与2013年芦山MS7.0主震和5级余震相似的逆冲型破裂特征,压应力轴方位与龙门山断裂带南段区域应力场一致。2013年芦山MS7.0地震后震中及附近的应力张量方差和b值长期处于低值状态,2022年芦山MS6.1地震前震中及附近出现了应力张量方差和b值的低值异常,表明芦山余震区处于较高的应力水平。分析认为:巴颜喀拉块体持续东向运动受到华南块体的阻挡,震中所在区域长期受挤压逆冲作用,从而使芦山余震区长期处于应力积累的状态,芦山MS6.1地震也是在这种动力学背景下发生的。
On June 1,2022,an MS6.1 earthquake struck Lushan Country,Ya'an City of Sichuan Province.The earthquake is another significant event that occurred in the aftershock zone of the Lushan MS7.0 earthquake on May 20,2013.To figure out the genesis and occurrence of the Lushan MS6.1 earthquake,the CAP inversion method is used to calculate the focal mechanism of the Lushan MS7.0 mainshock and its MS≥5.0 aftershocks.And the mechanical mechanism and the stress state in the source area before the Lushan MS6.1 earthquake are discussed based on the spatial and temporal distribution of the stress tensor variance and b value.The main insights are as follows:The focal mechanism of the Lushan MS6.1 earthquake is featured as a thrust rupture,which is similar to the feature of the focal mechanism of the Lushan MS7.0 earthquake and its MS≥5.0 aftershocks.The direction of the principal compressive stress is consistent with the regional stress field of the southern section of the Longmenshan fault zone.The stress tensor variance and b value around the epicenter of the Lushan MS7.0 earthquake are in a low state in a long period.What is more,shortly before the Lushan MS6.1 earthquake,in its focal area there appeared low-value anomalies of the stress tensor variance and b value,indicating that the Lushan MS7.0 earthquake aftershock zone had been keeping a higher stress level.The continuous eastward movement of the Bayan Har block is blocked by the South China block.Thus,the aftershock zone of the Lushan MS7.0 earthquake is under the action of the horizontal extrusion and thrust,which leads to the long-term stress accumulation in this zone.Hence in this dynamic background,the Lushan MS6.1 earthquake occurred.