山东苍山5.2级地震前深井地电观测网点异常及其特征
Anomaly Features of Deep-well Geoelectricity Observed Prior to M5.2 Earthquake in Cangshan, Shandong Province

对1995年9月20日山东苍山5.2级地震前8个深井地电台点观测资料进行整理分析，发现震前各测点均岀现了不同程度的异常反映。位于相互交汇的沂沭、苍尼两大断裂上的3个测点于震前26个月同歩出现异常；位于两大断裂之间的2个测点震前16个月同步出现异常；与震中有多条断裂相隔的2个测点震前13个月同步出现异常。异常突变峰值震前24个月在二大断裂交汇部位（近源区）测点出现，然后又以7个月和8个月的时间间隔在沂沭带（源外围）测点依次出现。距震中最近的测点和较远测点分别于震前111天和8天出现短临异常，其它测点在震前17~56天出现。对异常特征分析表明，异常出现的时间和形态变化，与震中距离、测点所处构造部位、构造背景及区域应力场主压应力方向有关。
In this study, we analyzed observation data recorded prior to the occurrence of an M5.2 earthquake in Cangshan county, Shandong province, which were recorded by eight deep-well geoelectric stations within a 100 km radius of the epicenter. The results reveal varying degrees of anomalies at all stations. Further analysis of these anomalies indicates that the anomalies appeared synchronously 26 months prior to the earthquake at three stations located at the cross section of the Yishu and Cangni faults; 16 months prior to the earthquake at two stations located between the two faults; and 13 months prior to the earthquake at two stations located several faults away from the epicenter. Our analysis of the anomaly features shows that their times of appearance and changes are related to the epicentral distance, tectonic position of the station, tectonic setting, and the direction of the principal compressional stress of the regional stress field. The research suggests that observations of deep-well geoelectricity networks are extracted directly from the internal bedrock and are significant for earthquake monitoring and prediction.