张北6．2级地震宝昌地震台地电异常特征及机制分析

The earth resistivity anomaly and its mechanism at Baochang Seismic Station before and after Zhangbei Ms 6.2 earthquake

首先分析了宝昌地震台地电阻率观测值曲线具有的长趋势变化以及规则年周期变化特征，为确定和提取前兆异常提供了正常变化的背景值和参考值。其次，通过去倾、傅立叶去年周期变化以及归一化月速率等方法，分析了1998年张北6．2级地震前后地电阻率异常特征，并利用相关理论尝试解释了异常产生的物理机制。归一化月速率法对于提取、分析短临异常，判断发震时间，较为理想；膨胀流体扩散（DD）模式适于解释宝昌地震台地电异常，而广泛扩容各向异性（EDA）模型适合解释该台地电阻率变化的各向异性。

The normal variation value curves of the earth resistivity observed at Baochang Seismic Station is analyzed. The variation is composed of long-term trends and annual periodic variation. The background values of the normal variation are obtained, which are used for confirming and extracting anomaly. Then original data are processed and analyzed by using different methods. The normalized monthly rate method is especially suitable to extract short-impending anomaly and determine the origin time. At last, the physical mechanism is applied to explain the produce of anomaly before and after Zhangbei Ms 6.2 earthquake. It is thought that using the DD model and the EDA model can explain the change processes of the earth resistivity anomaly and the anisotropy of the variation respectively.