On August 8, 2017, an Ms 7.0 earthquake hit Jiuzhaigou County, Sichuan Province, China. Before the earthquake, the AETA system was equipped with 6 monitoring stations in Jiuzhaigou County, Songpan County, Pingwu County, Qingchuan County, Maoxian County and Wenchuan County of Sichuan Province within a 200 km radius of the epicenter. With sliding principal component analysis (PCA) method, whose length of time window is 30 days, we analyzed the characteristics of electromagnetic disturbance of these six stations, and discussed the coand post-seismic changes of the electromagnetic field observed by the AETA system, and proposed a new impending seismic feature, namely the “anomaly band”. The results show that except the day of Jiuzhaigou Ms 7.0 earthquake, anomalous points appeared on monitoring station of Jiuzhaigou in the same period (5:00 am–6: 00 am) from the 5th day before the earthquake to the 15th day after the earthquake, and the anomalous value generally presented the trend of increase before the earthquake and decrease after the earthquake. Although anomalous points appeared on other monitoring stations, these points were scattered and the anomaly value was low. Within Two months after the abnormal band disappeared, there were no obvious band anomaly and no strong earthquakes.

2017年8月8日中国四川省九寨沟县Ms 7.0级地震前, 在震源200 km范围内的九寨沟、松潘、平武、青川、茂县和汶川布设AETA系统的6个监测台。采用窗口为30日的滑动主成分分析(principal component analysis, PCA)方法, 对6个台站的电磁扰动进行特征分析, 探讨九寨沟Ms 7.0级地震前后AETA系统观测的电磁场变化特征, 并由此提出一种新的临震特征, 即AETA电磁数据经滑动PCA方法处理后得到的“条带异常”。结果显示: 1) 除九寨沟Ms 7.0级地震发震当日, 九寨沟监测台于震前5日至震后15日, 每天在同一时段(5:00 am—6:00 am)出现异常点, 形成“异常条带”, 异常程度在震前大体上呈递增变化, 震后大体上呈递减变化; 2) 震源附近其他监测台也存在异常点, 但发布零散且异常程度较小; 3) 九寨沟Ms 7.0级地震“异常条带”消失后的两个月内, 未出现新的“异常条带”, 且无强震发生。