前震序列与一般小震群活动规律的探讨

研究前震序列的活动规律及其与一般小震群的区别,对于研究地震孕育过程及地震预报都是有益的。为此,我们处理了我国近十几年来资料较详细的17个地震,发现其前震活动是在主震前较早时间就开始的,它与波速变化似有某种对应关系。选择主震前适当的时间间隔,其中的前震频数一般随时间接近主震而按指数增长。并且,大地震的一个4级以上前震与一般小震群中的同量级地震发生前的应变释放速率是不同的。

A STUDY OF CERTAIN FEATURES OF A FORESHOCK SEQUENCE AND THAT OF AN ORDINARY EARTHQUAKE SWARM

To study certain features of the seismic activity of a foreshock sequence and their difference from that of an ordinary earthquake swarm will be of value to the study of the process of development of the main shock at its focus and to earthquake prediction. It is for this purpose that the detailed data,of 17 of the larger earthquakes that occurred within the last ten years or so in China,have been processed and analysed. The results show that the activity of the foreshocks begins at a comparatively early date before the main shock,that there secms to be some correlation between the foreshock activity and changes in the wave velocity ratio. If appropriate time intervals are chosen before the main shock,the number of foreshocks in an interval generally increases with time exponentially. Furthermore,a foreshock with magnitude over 4 of a large earthquake differs in the rate of strain release from that of an earthquake of the same magnitude of an ordinary earthquake swarm.