宁夏37度区地震活动初探

PRELIMINARY STUDY ON SEISMICITIES IN 37° AREA IN NINGXIA HU1 AUTONOMOUS REGION

本文利用选定的宁夏37度区域范围发生的历史强地震资料,及1966—1986年发生的M_L≥2.0级地震资料,对6级以上强地震的空间展布特征、周期特征、相关地震进行了初步探讨,发现该区历史上发生的4次7级以上强烈地震在时空序列上呈现一幅对称迁移活动图象,6级以上强地震的发生有明显的时间间隔规律,同时与华北大区域强地震活动关联较为密切。通过对现今小震活动分级按年度进行频次、平均震级的距平计算,发现该区小震活动在宁夏及邻区发生的6组(8次)5级以上中强震前1—2年,都出现过不同程度的“缺震”异常年份。在异常年份后,该区发生的4级地震具有预测预报宁夏及邻区中强以上地震的短期前兆“信号”作用。在对宁夏区内和邻区的报震时间上也表现出明显的差异。

This paper preliminarily studies the features of spatial spreading and periodic character of strong earthquakes with magnitude>6 and their related shocks using the historic strong earthquake data and the 1966-1986 earthquake (M≥2.0) data in the selected range of 37° area in Ningxia Hui Autonomous Region. It is found that four strong shocks with M>7 wi-thin this area in the history possess a pattern of symmetric migration in the time-space sequence. The occurrence of strong shocks with M>6 has a time-interval regularity that is closely re-lated to the strong earthquake activity in the large area of North China. Through calculating the annual frequency and average magnitude of recent small shocks, the author found that 1-2 years before 6 groups of moderately strong earthquakes (8 events) with M>5 in Ningxia and adjacent areas, there had appeared abnormal years of lacking shocks. After the abnormal years, the occurrence of shocks with M≈4 may be taken as a short-period signal for predicting mo-derately strong shock in or around Ningxia Hui Autonomous Region. But the earthquake oc-currence time predicted by such signals can be obviously different for Ningxia region and its adjacent areas