【摘要】 我国大陆地震多发生在１０～２５ｋｍ深处，在此部位的电性前兆异常，按穿透深度规律传输至地表已相当微弱。当同时考虑场兆的作用时（周硕愚，１９９３），由于电性异常区域的扩展，可大大增强大地电磁法监测地震活动的能力。一维和二维模拟计算结果与震前观测到视电阻率下降的事实相吻合（刘国栋等，１９８４），为此提供了极好的佐证。相应的物理机制是，在地震孕育过程中，因应力作用，岩石扩容，被流体充填，提高了异常区的导电性。更多还原

【Abstract】 Most earthquakes of the Chinese mainland occurred within the depth range of 10～25km which is usually called the seismogenic layer.According to the rule of penetration depth,the precursor of the electric anomaly which is transferred from the seismogenic layer to the Earth′s surface should be very weak.But ability of monitoring earthquakes can be greatly improved if the fleld precursor effect is taken into consideration because of expansion of the electric anomaly area.The results of one and two dimensional modeling computation are consistent with the observed fact that the apparent resistivity decreased befroe earthquakes.This provides the good evidence for our inference.The corresponding physical mechanism is that the conductivity of the anomaly area may be increased by the rock dilatation and fluid permeation due to the stress effect during the developing process of earthquakes.更多还原