1976年唐山大地震前后,距唐山不超过120公里的西集、宝坻、塘沽地电观测台,记录到自然电场双振幅超过标准误差6—20倍、电场矢量方向大致平行附近断裂带的周期性变化,其周期为半月、一月和半年,而京津地区的其它地电观测台均无此现象。这是与地震有关 Before and after the Tangshan earthquake in 1976, no more than 120 km away from Tangshan, Xizhi, Baodi, and Tanggu earth observation stations, the periodicity of double-amplitude of natural electric field more than standard error of 6-20 times and the direction of electric field approximately parallel to the fault zone was recorded Change, the cycle of half a month, January and half a year, and other geoelectric observatories in Beijing and Tianjin are not this phenomenon. This is earthquake-related