四川九寨沟MS7.0地震前地电阻率的异常变化
Earth-resistivity Anomalies before the Jiuzhaigou MS 7.0 Earthquake in Sichuan Province

四川九寨沟7.0级地震前，距离震中360 km的平凉井下地电阻率出现了持续1年的趋势异常，NS和EW测项异常幅度年变化率均大于背景值（正常年变化0.6%和0.4%），分别为1.1%、0.6%；2017年6月27-29日中国地震局台网中心、宁夏地震局、甘肃省地震局组成联合异常核实小组，对这组变化进行分析研判，确定是地下介质电性发生了变化，属于震兆异常。在震前20个小时平凉地电NS和EW两个测道日变化率分别为8.9‰、1.5‰，主震结束后，测值基本恢复到背景值。该次变化对地震预测有积极的研究价值。
Before the occurrence of MS7.0 earthquake near Jiuzhaigou county in Sichuan province, the earth resistivity measured in shallow wells at Pingliang seismological station, which is situated approximately 360 km from the epicenter, showed an abnormal trend for a year. The anomalous amplitude of NS and EW measuring channels showed annual variation rates of 1.1% and 0.6%, respectively, which were larger compared with the background value (0.6%~0.4% of the normal annual variation). The anomalous change was analyzed by a joint anomaly verification team comprising the China Earthquake Network Center, Earthquake Administration of Ningxia Hui Autonomous Region, and Earthquake Administration of Gansu Province from June 27 to 29, 2017. The analysis results revealed that change occurs in the resistivity of the underground medium, which is the seismic precursory anomaly. Twenty hours prior to the earthquake, the NS and EW channels showed daily variation rates up to 8.9‰ and 1.5‰, respectively. After the mainshock, the measured value basically returned to the background value. This study has a positive research value in predicting earthquakes.