2021年5月漾濞M_(S)6.4地震序列发震机理的应力分析  

Stress analysis for the seismogenic mechanism of the Yangbi MS6.4 earthquake sequence in May 2021

作　　者：李振月 李俊伦 姚华建[1,2] 王宝善 LI ZhenYue;LI JunLun;YAO HuaJian;WANG BaoShan(School of Earth and Space Sciences,University ofScience and Technology of China,Hefei 230026,China;Mengcheng National Geophysical Observatory,Hefei 230026,China;Institute of Geophysics,China Earthquake Administration,Beijing 100081,China)

机构地区：[1]中国科学技术大学地球和空间科学学院,合肥230026 [2]蒙城地球物理国家野外科学观测研究站,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1448-1459,共12页Chinese Journal of Geophysics

基　　金：科技部重点研发项目(2021YFC3000602);国家自然科学基金(U2139204)共同资助。

摘　　要：为了从应力的角度解释2021年5月漾濞M_(S)6.4地震序列的发震机理,本文开展了包括刻画断层结构,反演震源区应力场,研究应力场对断层的加载作用以及地震序列中较大地震对断层活动的库仑应力影响等4个方面的研究,具体的认识为,(1)相比于前人工作中利用区域台阵定位结果刻画的断层结构,结合布设在漾濞震源区的实时地震监测台阵捕捉的7905个余震位置和沿断层均匀分布的16个M3.5以上地震的震源机制,我们刻画了漾濞地震序列发震断层的精细结构:漾濞地震序列最主要的特征为NW向和NE向两组断层共同破裂,NW向断层为右旋走滑破裂,NE向断层为左旋走滑破裂;(2)利用震源区1°×1°范围内的90个历史震源机制反演了震源区的背景应力场,得到震源区为近南北向水平挤压,东西向水平拉张的走滑型应力状态,应力方位的不确定度很小,而主应力相对大小(R)的不确定度很大,为0.2~0.8;(3)分析了漾濞地震序列两组发震断层的稳定性,发现两组发震断层均为应力场作用下最易失稳的断层.此外,发生在两组断层上地震的震源机制分别与两个最易失稳断层的震源机制相似,说明了背景应力对断层行为的控制作用;(4)两组断层都在失稳的边缘,任一组断层上的较强地震活动产生的应力扰动都可能推动另一组断层造成失稳,因此两组断层的活动存在着复杂的相互影响,我们对此亦进行了库仑应力的计算和验证.To reveal the seismogenic mechanism of the May 2021 Yangbi M_(S)6.4 earthquake sequence from the perspective of stress,we have conducted research in the following four aspects:characterizing the fault structure,inverting for the stress field in the source region,studying the loading effect of the background stress regime on the seismogenic faults,as well as studying the Coulomb stress effect of larger earthquakes on fault activities.(1)combining the locations of 7905 aftershocks captured by the real-time seismic monitoring system deployed in the Yangbi area and the 16 M≥3.5 focal mechanisms which evenly distributed along the active faults,we characterized the detailed structure of the seismogenic fault for the Yangbi earthquake sequence.Compared with the previous characterization results using the regional sparse array,our result reveals much more details.The main feature of the Yangbi earthquake sequence is the simultaneous ruptures of the two sets of faults,one trends in the northwest direction with dextral strike-slip,and the other trends in the northeast directional with sinistral strike-slip.(2)The tectonic stress regime in this area was estimated from 90 historical focal mechanisms within 1°×1°.The result shows that the focal region is strike-slip stress state of nearly north-south horizontal compression and east-west horizontal tension.The uncertainty in the stress orientation is relatively small,while the uncertainty in the relative magnitude(R)of the principal stresses is rather large,ranging from 0.2 to 0.8.(3)We analyzed the stability of both sets of the faults associated with the Yangbi earthquake sequence,and it is found that both seismogenic fault systems are prone to slip under the regional tectonic stress regime.In addition,the focal mechanisms of Yangbi sequence are similar with those of the most unstable faults,which indicates that the rupture behavior is controlled by the local stress regime.(4)Both sets of faults are rather susceptible to rupture,and the stress disturbance resulted by the

关 键 词：漾濞地震序列 震源机制 应力 断层稳定性 应力触发 

分 类 号：P315[天文地球—地震学]