中国主要地震活动区的地震间隙分布

EARTHQUAKE INTERVAL DISTRIBUTION OF MAIN SEISMIC AREAS IN CHINA

结合地震间隙和强度变化分析了本世纪全国及国内主要地震活动区中强以 上地震活动特征，间隙大多在５．５ａ内,一半以上在２．５ａ内,最大间隙近１８ａ.５０年代 以后全国７．５级以上和７．０级以上、青藏块体７．０级以上地震活动及近２０ａ来台湾 ７．０级以上、华北和四川６．０级以上地震活动明显减弱，２０－３０年代青藏块体北部大 震的活动影响一直持续到７０年代，５．０－６．５级地震活动自８０年代明显增强，云南 ７０年代后形成的地震活动高潮实际上从６０年代就开始增强，华北和台湾地区表现 了强震前活动增强而甘宁青地区表现了强震后活动衰减的典型过程，制约我国地震 活动的大三角应力场、东部应力场和全球应力场具有长期稳定的２０ａ周期性，后面的 应力场依次滞后于前一个应力场约１／４个周期，前两者起主导作用，青藏块体东北缘 的地震活动除受东部应力场的影响外，还与青藏块体地壳物质东流的重要作用有关， 今后几年要特别注意四川和甘宁青６．０级以上、甘肃地区５．０级以上及新疆７．０级 以上地震。

Combining the variations of earthquake intervals and magnitudes. the activity features of mod- erate or stronger earthquakes in whole country and the main seismicity areas in China during this century are analyzed Most of intervals are within 5.5a, more than half are within 2.5a, and the maximum valve of interval is near 18a. After 1950s, activity weakened obviously for earthquakes of M 7.5 and M 7.0 all over China, M 70 in Qinghai-Xizang block ( QXE), and after 1670s, it did so for shocks of M 7.0 in Taiwan, M 6.0 in North China, and M6.0 in Sichuan. The influence of strong earthquakes which occurred in northern part of QXB from 1920s to 1930s on the seismicity of this region ended in 1970s, then, activity of 5.0 M 6.5 earth- quakes strengthened from 1980s clearly . The high tide of Yunnan seismicity formed after 1970s, in fact, was enhanced from 1960s. The typical process of strengthening before strong earthquakes is showed in North China and Taiwan, and that of attenuation after strong earthquakes is showed in Ganst-Ningxia-Qinghai(GNQ), The stress field of great triangle region, stress field of east part and the global scale stress field which are controlling the seismicity all over China have a stable pe- riod about 20a for a long time, while the later delayed about 1/4 period for the former in proper order, and the two former played a leading role. The seismicity along the eastern and northern edge of QXB include the important roll of QXB crust matter flowing toward east besides influence of stress field in east part. We should follow with interest the possibility of Sichuan M 6. 0, GNQ M , Gansu M and Xinjiang 7.0 earthquakes in future years.