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从地震观测资料出发,分析了几次晚期强余震前后小震活动的震中分布。给出1966年3月8日邢台地震和1975年2月4日海城地震之后三次晚期强余震前后小震活动分布特征。表明在晚期强余震之前的小震分布沿着一定的方向线,这些较小前震被称为“次级前震”,晚期强余震就发生在这些次级前震分布的方向线的一端。在空间上这些次级前震靠近强余震发生的部位,那里可能是构造的闭锁
Based on the seismic observation data, the epicenter distribution of small earthquakes before and after several strong aftershocks was analyzed. The distribution characteristics of small earthquakes before and after the third-period strong aftershocks after Xingtai earthquake of March 8, 1966 and February 4, 1975, Haicheng earthquake are given. This indicates that the small earthquakes before the late strong aftershocks are distributed along a certain direction line. These smaller foreshocks are called “secondary foreshocks.” Late strong aftershocks occur at one end of the direction line of these secondary foreshocks. These secondary foreshocks are spatially close to the site of the strong aftershock where there may be structural blockades