2017年8月8日四川省九寨沟县发生M_S7.0地震，成都地震基准台距此次地震震中约255km，震前该台地磁谐波振幅比出现趋势性异常。对成都台GM4磁通门磁力仪秒数据进行谐波振幅比计算，结果显示，谐波振幅比在九寨沟M_S7.0地震前表现出下降—转折—恢复上升的异常变化形态，地震发生在异常恢复期，同时，异常表现出由长周期向短周期迁移、SN向与EW向变化不同步的特征，芦山M_S7.0地震前成都台地磁谐波振幅比亦呈现了相似的异常变化特征。

On August 8, 2017, an M_S7.0 earthquake occurred in Jiuzhaigou County, Sichuan Province. The Chengdu seismic station is 255km away from the epicentre, and there were tendency anomalies of the amplitude ratios of geomagnetic harmonic wave of the station before the M_S7.0 earthquake. Based on the 1-second sampling data derived from the GM4 magnetometer of the Chengdu seismic station, the temporal variation of the geomagnetic harmonic wave amplitude ratios were analyzed, and the results show that the anomalous characteristics had a down-turning-recovery tendency before the M_S7.0 earthquake, and there was asynchronization between long-period and short-period, and also between north-south direction and west-east direction. The similar variation appeared for the amplitude ratios of the Chengdu seismic station before the M_S7.0 Lushan earthquake.

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川滇国家地震监测预报实验场项目（2016CESE0102）、中国地震局震情跟踪定向工作任务（2018010410）共同资助