2021年阿鲁科尔沁旗ML5.1地震精定位及发震构造研究

The Accurate Location and Seismogenic Structure Analysis of 2021 Aruhorqin Banner ML5.1 Earthquake

摘要:

2021年10月15日内蒙古自治区阿鲁科尔沁旗发生M_L5.1地震。为更好地了解本次地震的发震构造,应用hypoDD方法对地震序列中34个地震进行精定位,分别采用CAP方法对主震、Focmec方法对M_L2.0以上余震计算震源机制解,根据序列震源机制解进行应力场反演,并对地震序列进行断层面拟合。精定位结果显示,主震的震源深度为19.89km,定位后的31个地震分布更加集中,走向为ES-WN向,地震序列是一次由深部向浅部的破裂。震源机制解结果显示,主震震源机制解节面Ⅰ的走向、倾角和滑动角分别为134°/86°/-8°,节面Ⅱ的走向、倾角和滑动角分别为224°/82°/-177°,矩震级为4.51,是以走滑型为主的地震。结合余震NW向展布,认为节面Ⅰ对应发震构造。断层拟合结果显示,断层走向142.54°,倾角85.49°,结果与震源机制节面Ⅰ的走向和倾角相近,两者的走向均为NW向。区域应力场结果显示,最大主应力轴σ₁的走向为93.51°,倾伏角为8.69°,最小主应力轴σ₃走向为186.49°,倾伏角为18.81°,表明该区域的断层应力主要以走滑性质为主。综合上述结果并结合本地区的地质构造特征,认为此次地震的发震构造可能与一条NW向隐伏断裂有关。

Abstract:

An earthquake with a magnitude of M_L5.1 occurred in Aruhorqin Banner,Inner Mongolia Autonomous Region,on October 15,2021. To enhance the understanding and analysis of the seismotectonic structure of this event,this study employs a comprehensive methodology. The hypoDD method is utilized to accurately relocate 34 earthquakes,while the CAP method is applied to determine the focal mechanism of the main shock. The Focmec method is used for aftershocks with magnitudes above M_L 2.0. Subsequently,the stress field is inverted based on the focal mechanisms of the earthquake sequence,and fault fitting is performed on the relocated events. The relocation results indicate that the earthquake source depth is 19.89km. The distribution of 31 relocated earthquakes is more concentrated,exhibiting a trend from southeast to northwest,with the rupture sequence propagating from deeper to shallower depths. The focal mechanism results for the main shock reveal that the strike,dip,and rake angles of nodal plane I are 134°,86°,and-8°,respectively,while those of nodal plane II are 224°,82°,and-177°,respectively. The moment magnitude (M_W) is determined to be 4.51,indicating a predominantly strike-slip event. Given the northwest distribution of aftershocks,nodal plane I is inferred to correspond to the seismogenic structure. Fault fitting results show that the fault strike is 142.54° and the dip angle is 85.49°,which aligns closely with the direction and inclination of focal mechanism plane I,both trending northwest (NW) . Regional stress field analysis indicates that the maximum principal stress axis (σ₁) trends at 93.51° with an elevation angle of 8.69°,while the minimum principal stress axis (σ₃) trends at 186.49° with an elevation angle of 18.81°. These results suggest that the fault stress in this region is predominantly characterized by strike-slip motion. Based on the above findings and the seismic geological structural characteristics of the region,it is inferred that the seismogenic structure of this earthquake is a northwest-trending concealed fault.