1976年我国大陆地震活动高潮时段过后,在地震监视预报中又遇到一些新问题。就华北而论,1978年4至6月、1979年6至8月和1981年7至9月,曾出现过三次中等地震的成丛活动(地震在某一时间段连续发生的现象),各次均包含6级左右地震,这是1976年之后五年来地震活动最突出的三个时段。与此同时及其前后的一段时间,前兆场也发生了较为突出、较为广泛的异常变化,我们把这种成丛地震活 After the upsurge of the earthquake activity in mainland China in 1976, some new problems have been encountered in the earthquake monitoring and forecasting. In the case of North China, three moderate earthquakes (earthquakes that occur continuously over a period of time) have occurred in April-June 1978, June-August 1979 and July-September 1981 respectively All of them contain about 6 earthquakes, which are the three most prominent seismic activities in the five years after 1976. At the same time and around the time, the precursory field also occurred more prominent, more extensive abnormal changes, we put this clump of earthquakes