| Abstract: | We have compared the Haicheng foreshock sequence with several earthquake swarms which occurred in its neighborhood. The spatial distribution of the earthquakes is relatively concentrated. For the most part, the events occurred within a few kilometers of 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 compared to the Haicheng foreshock sequence. This feature could thus not be used to identify a foreshock sequence. The temporal distributions of foreshocks and swarms are quite similar in some cases. This is again not a definite criterion for identifying foreshocks, but is worthy of further study. Thus, no definite criterion for identifying foreshock sequences has been found. However, some earthquake swarms may be recognized in their later stage.Finally, we introduced a magnitude sequence with gaps which can be used to see whether a large event is still forthcoming. This method (in conjunction with other methods) could be used in areas prone to large earthquakes, immediately before a large event, to improve the probability of predicting the occurrence of a large event. We also report that the temporal distribution of all the sequences showed a 12-hour recurrence pattern that corresponded with the earth tides, indicating that tidal forces might be influencing foreshocks and earthquake swarm occurrence. |
