【摘要】 本文分析了华北地区(30°—42°N,105°—124°E)自16世纪以来8次7.5级以上大地震发生之前的地震活动图象.发现在这些大地震发生之前的若干年(绝大多数不超过20年),都表现出一个M≥4(3/4)地震在某一范围內相对较集中活动的区域,然后在该区中部或边缘发生大地震。 唐山7.8级地震前,随着大地震发生时间的逼近,M_s≥4.0地震的震中分布,在大范围活动的基础上,分阶段地逐步自外围向主震震中收缩,然后发生大地震。这种地震活动图象的演变过程可分成若干阶段的现象,对于研究震源性质、地震孕育过程和中长期地震预报等,可能具有一定意义。更多还原

【Abstract】 The seismicity patterns before 8 great earthquakes with M>7.5 of North China (30-40°N, 105-124°E) occurred since the 16th century have been analyzed. It wasfound that before any of them, earthquakes with M≥43/4 usually occurred in a periodof several years (in most cases not longer than 20 years) within a rather restricted region. Then finally the major earthquake took place at the center or near the edge of that region.Before the 1976 Tangshan Earthquake of M=7.8, the epicenters of earthquakes of M≥4.0 within such a region as above-mentioned gradually came near to the epicenter of the great Tangshan Earthquake by stages as time approached its outbreak. Such a fact of variation of seismicity pattern in stages before a great earthquake probably contains certain implications related to the study of focal properties, seismogenic process, long-term earthquake prediction and so on.更多还原