2021年9月4日新疆皮山MS 5.1和9月5日叶城MS 5.0地震总结

系统梳理2021年9月4日新疆皮山M_S 5.1和9月5日叶城M_S 5.0地震发生前地震活动异常特征、地球物理观测异常以及区域构造情况，结果如下：①地震活动异常：皮山M_S 5.1地震前出现前兆震群活动、阿图什至皮山4级地震平静、库车—沙雅4级地震窗口以及地震发生率指数异常；②地球物理观测异常：2项异常，其中形变1项，电磁1项，但与此次地震活动相关性较低；③震源机制：泽普断裂距皮山M_S 5.1和叶城M_S 5.0地震最近，间距分别约15 km和3 km，震源机制解显示2次地震均为逆冲型破裂；④序列分析：此次地震活动序列类型为震群型，主震前存在明显的前震活动，余震较为丰富，余震活动呈阶段性衰减特征。综合分析认为，2021年9月皮山M_S 5.1和叶城M_S 5.0地震组成震群型地震序列，震前地球物理观测异常较少，地震活动异常主要对发震地点具有预测意义。

About Pishan MS 5.1 and Yecheng MS 5.0 earthquakes on Sep.4 to Sep.5, 2021, Xinjiang

Two earthquakes with M_S≥5.0 occurred in Pishan and Yecheng of Xinjiang Uygur Autonomous Region on Sep.4 to Sep.5, 2021. This paper systematically summarized the historical seismicity, geophysical observations before the two events and tectonic background. The results show that: ① Seismicity anomalies: there are precursory earthquake swarms before the Pishan M_S 5.1 earthquake, quiescence of earthquakes with M_S≥4.0 from Artux to Pishan, earthquake window of Kuqa to Shaya, and seismicity rate; ② Geophysical observations: there are 2 geophysical anomalies include deformation and electromagnetism, while both anomalies are less related to these earthquakes; ③ The Zepu fault is the closest fault to the Pishan M_S 5.1 and Yecheng M_S 5.0 earthquakes, which is about 15 km and 3 km away from the two earthquakes, respectively, and the focal mechanism solution shows that both M_S≥5.0 earthquakes are thrust earthquakes; ④ The sequence is a swarm, there are obvious foreshocks before the mainshock, and there are abundant aftershocks, and the sequence activity shows the characteristics of phased attenuation. Comprehensive analysis shows that the Pishan M_S 5.1 and Yecheng M_S 5.0 earthquakes in Sep. 2021 are composed of a swarm, and there are few geophysical anomalies observed before the earthquakes, and the seismic activity anomalies are mainly predicted by location.