关键词: 地震相关活动, 地震趋势, 中国西部, 大华北

Abstract: Based on the analysis of temporal and spatial distribution of great earthquakes (M_S≥7.5) in West China since 1900, the correlation between great earthquake activity in West China and strong earthquake (M_S≥6.0) activity in North China is studied. The result shows that the activity of great earthquakes in West China is controlled by the seismotectonics of the region. Seismic activities in each active period of great earthquake in West China almost occur successively or in cluster within the same sub plate, but other tectonic units in surrounding areas still keep relatively quiet. This may indicate that a seismically active block is an active tectonic unit confined by boundary faults of various strikes. The activation of strong earthquake on a boundary fault will affect the stability of the other boundary faults within the same tectonic unit, and it may trigger strong earthquake activities on those boundary faults. Seismic activities in China have the characteristics of oriented migration. In the first active period, strong earthquakes concentrated mostly in Xingjiang sub-plate, northwest China. In the early stage of the second active period, the earthquake site migrated to the southwest of Qinghai-Tibet sub-plate, while in the later stage it migrated to the southern part of the South-north seismic belt. In the third active period, the earthquake site migrated to the northwest of Qinghai Tibet sub plate. The earthquakes have no repeatability in spatial distributions. When a series of earthquakes occur in a tectonic block, the last earthquake always migrates from the block and occurs in another relatively stable block, and hence is useful for determining the occurrence site of the next series of earthquakes. The activity of strong earthquakes in North China is basically synchronous with the activity of great earthquakes in West China, but the beginning time of strong earthquake activity in North China is later than that in West China. Therefore, though the third active period of great earthquakes in West China has begun now, the probability of the successive occurrences of strong earthquakes (M_S≥6.0) in North China in the near future is very low.

Key words: correlation of seismicity, seismic tendency, West China, North China