海城地震前震系列与震群——兼论前震系列在地震预报中的一种功能

对比了海城前震系列与其周围同期震群的异同.两者的震源空间分布都比较集中,一般只有几公里的尺度.发震机制都比较稳定.但有些震群在其主要地震发生后,机制变化较显著,借此有可能识别一部份震群.但也有些震群其机制的稳定性始终不比海城前震系列差,因之借此无法识别前震系列.频次的分布两者也有非常相似的震例.总的印象是有些震群在晚期有可能识别,但未发现有确认前震(系列)的肯定判据.这一初步的结论仅仅是由于我们分辨技术的局限,抑是具有成因上的深刻含义是很值得思考的.最后引入了震级序列的缺震特征,借此可以判断系列的高潮是否已经渡过.这对(从其他证据认识到的)具有大震危险的地区,利用前震系列来改善大震临震时刻的机率性判断是有用的.注意到频次分布中有相隔12小时的低值点,对比就地的固体潮具有较好的同步性,说明固体潮可能对前震系列以及震群具有触发作用. 

THE FORESHOCK SEQUENCE OF HAICHENG EARTHQUAKE AND EARTHQUAKE SWARM--THE USE OF FORESHOCK SEQUENCES IN EARTHQUAKE PREDICTION

We have compared the Haicheng foreshock sequence with several earthquake swarms occurred in its neighborhood. Their spatial distribution of earthquakes was relatively concentrated. For the most part, the events occurred within a few kilometers from each other. The focal mechanisms are comparatively stable. However, there are several swarms in which the variations of focal mechanisms are quite obvious after the occurrence of the largest event of the sequence which would allow it to be recognized as a swarm. However, there are also swarms whose focal mechanisms are no less stable throughout the sequence as compared with that of the Haicheng foreshock sequence. So this feature could not be used to identify foreshock sequence. The temporal distributions of foreshocks and swarms are quite similar in some cases. This is again not a definite criterion for discriminating foreshocks and is only within our present ability, but is worthy of further study. Thus in general, no definite criterion for identifying foreshock sequence has been found. Only for some earthquake swarms may be recognized in their later stage.Finally, we introduced a magnitude sequence with gaps which, may be used whether a large event is still forthcoming. This method (in conjunction with other methods) could be of use in areas prone to large earthquakes immediately before a large event to improve determining the probability of a large event occurring. We also note that the temporal distribution of all the sequences showed a 12 hour recurrence pattern that corresponded with the earth tides, showing that tidal forces might be influencing foreshocks and earthquake swarm occurrence.