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中低纬度地磁场Z分量S_q变化极小值出现的时刻常常被用作预报地震的前兆(即“低点位移”法)。本文指出一种能引起“低点位移”的非地震原因:——行星际磁场北向分量的变化引起磁层大尺度电场的变化;这个变化电场透过阿尔芬层,进入内磁层,并在电离层中形成一个特征的电流体系,使S_q电流体系发生畸变,电流涡的焦点发生位移,从而引起地面磁场Z分量极小值地方时的改变。这个过程所引起的“低点位移”有时可以超过1小时。所以在用“低点位移”法预报地震时,应该考虑行星际磁场的状态,排除非地震起因的磁异常。
At low and medium latitudes, the moment when the minimum component of the Z component S_q changes occurs is often used as a precursor to forecasting the earthquake (ie, the “low displacement” method). This article points out a non-seismic cause of “low-point displacement”: - changes in the north component of the interplanetary magnetic field cause changes in the large-scale electric field in the magnetosphere; this changing electric field penetrates the Alphin layer and enters the inner magnetosphere, The formation of a characteristic current system in the ionosphere distorts the S_q current system and the focus of the current vortex shifts, causing a change in the Z component of the ground magnetic field to a minimum. The “low shift” caused by this process can sometimes exceed 1 hour. Therefore, when using the “low displacement” method to predict earthquakes, the state of the interplanetary magnetic field should be considered and the magnetic anomalies other than earthquakes should be excluded.