唐山大地震后华北地区中强震活动空间分布

SPATIAL DISTRIBUTION OF MODERATE EARTHQUAKES IN NORTH CHINA AFTER TANGSHAN EARTHQUAKE

1966—1976年是华北地区强震集中发生的阶段。唐山地震后,溧阳—介休等地震带是华北地区地震最为活跃的地带。结合前人的研究成果和唐山地震后华北地区ML≥5级地震空间、时间分布特征,认为唐山地震后华北地区中强地震的主要活动方向为北西向,地震活动的主体区域伴随着时间的推移在不断改变。中强地震活动具有成丛发生的特点,地震活动水平在减弱的同时,逐渐从有序状态向无序状态演化。这些现象表明华北地区的中强地震活动已进入相对平静的阶段。

In North China,the strong earthquakes concentratively occurred in 19661976 after the 1976 Tangshan earthquake, some NWdirection seismic belts, like the LiyangJiexiu seismic belt, etc., become the main active zones in North China. Combined with the predecessors' research result and the temporalspatial distribution characteristics of M\-L≥5 events in the North China area after the Tangshan earthquake, it is thought that NW is the principal direction of moderate seismicity after the Tangshan earthquake, and main active zones of moderate earthquakes have been changing with the process of time. The moderate earthquakes occurred in cluster; and companied with the weakening of the activity level, the seismicity became disordered. These phenomena indicate the moderate earthquake activity has come into a comparatively quiet period in North China.