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.