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通常4．0级地震，一般只有几天较弱的电磁辐射前兆异常，反映范围一般也仅几十公里。而1995年7月20日涿鹿4．0级地震，其震前电磁异常却非常明显并出现的时间较早，震后信息较强，反映范围也较大，在约16～140km为长轴的近NW向区域内，前兆资料显示了一个由弱变强．再起伏减弱到逐步消失的过程；异常参数重现了方向性、频率升高变化等特征。信息偏强和持续时间较长的原因，可能与震源很浅和一系列的小震活动有关。
Usually 4.0 earthquake, generally only a few days weaker EMF precursory anomalies, reflecting the general range is only tens of kilometers. The July 20, 1995 Zhuolu 4.0 earthquake, the electromagnetic anomalies before the earthquake was very obvious and appear earlier, post-earthquake information is strong, reflecting the larger, at about 16 ~ 140km for the long axis Near NW, the precursory data showed a weakening. The ups and downs weaken to the gradual disappearance of the process; abnormal parameters to reproduce the characteristics of the directionality, frequency changes and so on. The reasons for the stronger information and the longer duration may be related to the shallow source and a series of small earthquakes.