摘要
2017年巴东M4.3地震序列为一发生在褶皱构造翼部的地震活动.地震精定位结果显示,整个地震序列呈NE向展布,震源深度较浅,M4.3和M4.1地震的震源深度分别为3.8km和2.4km.地震序列表现出NW浅、SE深的特征.震源机制解反演结果表明,两次较大地震的发震节面走向NEE,倾向SE,运动性质为走滑.震中区断裂构造分析发现,没有与发震节面吻合的断裂构造.结合地震定位结果和地质剖面分析,M4.3地震发生在三叠系岩溶及裂隙发育的厚层灰岩中,而M4.1地震及大多数小震活动则主要发生在巴东组红层(软弱滑脱层)中.地震发生时,三峡水库正处于低水位腾库容期间,库水卸荷使得库区原来由于荷载压实作用产生的压应力出现了局部回弹,进而引起部分裂隙的扩张,造成部分裂隙发育的岩体发生失稳滑动.此外,裂隙的扩张也为流体的渗透扩散提供了有利通道.流体渗透扩散一方面使得孔隙压力增大,有效应力降低;另一方面则使得软弱地层发生软化泥化,使得岩体发生顺层或切层的失稳滑动,造成了地震的发生.
The Badong M 4.3 earthquake sequence in June 2017 occurred in a fold structure.The earthquake relocation results show that the sequence is distributed along the NE-trending axis and the seismic source scale is estimated to be about 1.8 km in length and 1.3 km in width.The vast majority of the earthquakes are concentrated in the shallow crust of 2~3 km,and the focal depth of M 4.3 and M 4.1 earthquakes are 3.8 km and 2.4 km,respectively.The focal profiles reveal that the nodal plane dips to SE.Moment tensor solutions show that the two larger events occurred along the NEE-striking nodal plane.The parameters of the best focal mechanisms are as follows,strike 67°,dip 45°,rake 177°for the M 4.3 earthquake,and strike 62°,dip 63°,rake 173°for the M 4.1 earthquake.It is easy to find that the two events are controlled by the NEE-trending strike-slip movement.According to the analysis of the fault structures in the epicenter area,there are no faults consistent with the seismogenic nodal plane.Based on the earthquake location results and geological conditions,the M 4.3 earthquake occurred in the thick Triassic limestone with developed karst,while the M 4.1 earthquake and most of the micro-small earthquakes occurred in the Badong formation with weak slip layers.The sequence occurred at the low water level of the reservoir,and the water unloading makes the local rebound of the stress.It causes the expansion of some fissures,thereafter leads to the unstable sliding of the rock mass.In addition,the expansion of fissures provides favorable channels for the water permeation and diffusion.On the one hand,fluid permeation and diffusion makes the pore pressure increase and effective stress decrease.On the other hand,the soft stratum is softened and muddy,which causes the rock mass to slip in bedding or cut layer and tiggers the earthquakes.
作者
李井冈
张丽芬
廖武林
赵艳南
魏贵春
杨捷
陈玮
LI JingGang;ZHANG LiFen;LIAO WuLin;ZHAO YanNan;WEI GuiChun;YANG Jie;CHEN Wei(Institute of Seismology,China Earthquake Administration,Wuhan 430071,China;Institute of Geophysics,China Earthquake Administration,Beijing 100081,China;Three Gorges Group Corporation,Yichang Hubei 443000,China)
出处
《地球物理学报》
SCIE
EI
CAS
CSCD
北大核心
2018年第9期3701-3712,共12页
Chinese Journal of Geophysics
基金
中国地震局地震研究所基本科研业务费专项资助项目
中国地震局地壳应力研究所基本科研业务费专项资助项目(IS201616254)
国家自然科学基金项目(41572354
41772384)共同资助
关键词
三峡水库
双差定位
软弱夹层
卸荷回弹
流体渗透
Three Gorges reservoir
Double-difference algorithm
Interlayer of soft and hard rock
Unloading and rebound deformation
Fluid infiltration
