1989年大同地震的前兆特征及孕震过程

THE PRECURSORY CHARACTERISTICS AND SEISMOGENIC PROCESS OF THE DATONG EARTHQUAKE IN 1989

自1976年和林格尔6.3级地震之后,晋冀蒙交界地区M_L≥4地震有一个由西向东总体迁移的过程,小震活动自1985年以后形成空区,1987年以后形成条带。最早的前兆异常开始于1985年前后,并分布在空区内。以一批断层位移异常为标志的中期异常开始于1987年5、6月份,还有少数地下水位及地电阻率异常,全部分布在空区外围。短期异常开始于1989年3月,以地下水动态、水化、地磁异常为最多,兼有测震、地形变异常,其中地磁异常主要分布在空区的内部及其边缘地区,其它异常沿山西构造带和燕山构造带延伸较远。本文根据地震活动及前兆异带演化的阶段性推测了大同地震的孕育过程。

After the Helingeer 6.3 earthquake in 1976, the earthquakes with Ml≥4 occurred on the border land of Shanxi, Hebei and Inner Mongolia showed, in general, a migration from west to east, the small earthquake activity formed a gap after 1985, and formed a band after 1987, the earliest precursory anomalies emerged round about 1985 and distributed inside the gap. The mid-term anomalies marked by a set of fault displacement anomalies started in May and June of 1978, a few anomalies of groundwater level and earth resistivity appeared as well, and all these anomalies distributed outside the gap. The short-term anomalies started in March of 1987, most of which were anomalies of groundwater regime, hydrochemistry and geomagnetism, and there were anomalies of seismomitry and deformation as well. Among them, geomagnetic anomalies mainly distributed inside the gap and its boundary region, the other anomalies extended farther along Shanxi tectonic zone and Yanshan tectonic zone. In this paper, the seismogenic process of the Datong earthquake has been inferred based on the stages of seismic activity and precursory anomalies development.