2021年10月15日,内蒙古赤峰市阿鲁科尔沁旗发生4.7级地震,该地震是继2003年8月16日阿鲁科尔沁旗5.9级地震后,该区发生的第二次中等以上地震。使用CAP方法获取本次地震的震源机制解,将其与2003年5.9级地震的震源机制解比较发现,两次地震震源机制解结果基本一致,节面Ⅱ走向均为NW,且两次地震余震序列走向均为NW向展布,结合地质构造资料,判定两次地震的发震构造均为水泉子沟—天山口断裂。通过对2012年以来震源区及其附近区域的22个M_L≥3.5地震的可靠震源机制解的研究分析,发现通辽至阿鲁科尔沁旗一带震源机制解类型均为走滑型,应力场反演结果显示该区应力场受NNW向拉张和NEE向挤压联合作用,应力形因子R为0.7,表明近EW向的中间应力轴也具有拉张性质,构造环境以拉张作用为主。本次4.7级地震可能是在NNW向和近EW向拉张以及NEE向挤压的作用力下,水泉子沟—天山口断裂发生正走滑错动形成的一次中等强度地震。

On October 15,2021,a M_S4.7 earthquake occurred in Arhorchin Banner,Chifeng City,Inner Mongolia. It was the second moderate earthquake in this area since the M_S5.9 earthquake in Arhorchin Banner on August 16,2003. The focal mechanism solution of this earthquake was obtained by CAP method. Compared with the focal mechanism solution of the 2003 M_S5.9 earthquake,it was found that the focal mechanism solutions of the two earthquakes were basically consistent. The strikes of nodal plane II are NW,and the strikes of the two earthquakes are respectively NW. Combined with geological structure data,it is determined that Shuiquanzigou-Tianshankou fault is the seismogenic structure of two earthquakes. In our study,the reliable focal mechanism solutions of 22 M_L≥3.5 earthquakes in and around the focal area since 2012 are obtained. We find that the focal mechanism solutions in Tongliao-Arhorchin area are all strike-slip type. The inversion results of stress field show that the stress field in this area is jointly affected by the NNW tension and NEE compression. The stress shape factor R=0.7 suggests that the intermediate stress field is nearly in EW direction,with tensile properties,and the tectonic environment is mainly tensile. The M_S4.7 earthquake may be a medium-intensity earthquake caused by strike-slip dislocation of Shuiquanzigou-Tianshankou fault under the action of tension in NNW and EW direction and compression in NEE direction.

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中国地震局地震科技星火计划(XH20015Y)、震情跟踪定向工作任务(222010132、2022010135)共同资助