1990年乌苏5.2级地震前地下流体异常

１９９０年乌苏５．２级地震是北天山地区地下流体观测网改造以来，发生在监视区内的第一次中强地震。地震前出现了大面积、多井孔的地下流体异常，显示出了异常在空间上的一些变化。（１）震前异常形态复杂多样。由于不同的观测井其水文地质条件、水文地球化学环境以及观测参数本身的物理化学性质不同，表现出的异常形态也各不相同。另外，异常井孔的受力方式和受力性质的不同也是形成不同异常形态的重要原因。（２）位于震中区的观测井出现异常的比例显著高于外围地区；震中区异常出现时间较晚，外围地区异常出现较早，表现出异常从外围向震中迁移的变化图像。（３）与地震震中处于同一构造带的观测井（泉）容易受到震源应力的牵动和影响，出现异常的可能性大。

GROUND LIQUID ANOMALY BEFORE 1990 WUSU M5. 2 EARTHQUADE

The Wusu M5. 2 earthquake in 1990 has been the first moderate earthquake which occurred in the monitoring region since transformation of ground liquid observation network in North Tianshan region. The ground liquid anomalies appeared in large area and many wells before the earthquake. It shows some variations of the anomaies in the space. (1) the anomalous forms are complicated and various before the earthquake. For the different observing wells,because its hydrogeologic conditions and hydrogeochemistry settings are dirrerent,the anomalous forms are different. In addition, different methods and characters of the force acted on the wells also are the the main reasons that cause various anomalous forms. (2) the observing wells in the epicentre area are more than that in its periphery,and the anomalies in the epicentre area appeared later than that in its periphery. It is shown that the anomalies migrated from periphery to the seismic center. (3) Because the observing wells(springs)located in the same tectonic zone with the earthquake are easy to be affected by the earthquake,the Probability that anomalies would appear in these tveds is bigger.