SE1SMICITY PATTERN BEFORE GREAT EARTHQUAKES IN NORTH CHINA

The seismicity patterns before 8 great earthquakes with M>7.5 of North China (30-40N, 105-124E) occurred since the 16th century have been analyzed. It wasfound that before any of them, earthquakes with M43/4 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 M4.0 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.