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用 P、S波振幅比方法反演了 1988年 11月 2 2日肃南 5 .7级地震序列的震源机制 ,计算了对应的 P轴 T轴。结果表明 ,前震的一组节面比较集中且与主震断层面大体一致 ,其主压应力轴也表现出相对的集中。而余震 (以及以后发生在该地区的一些小震 )的断层面解则比较散乱 ,但总体上仍与该区的主要断层保持大体一致 ,但是余震的 P轴和 T轴则表现更大的散乱。由此我们可以认为 ,中强地震发生前震源区微震震源机制的相对一致性是发震断层在区域应力场作用下应力集中的临震表现。
The P and S wave amplitude ratio method was used to invert the focal mechanism of the Sunan MS 5.7 earthquake sequence on November 22, 1988 and calculate the corresponding P-axis and T-axis. The results show that the set of sections of the foreshock is relatively concentrated and generally consistent with the fault plane of the main shock, and its principal compressive stress axis also shows a relative concentration. The aftershocks (and some minor earthquakes that occurred in the area later) are more scattered but still generally consistent with the major faults in the area, but the aftershocks show more scattered P-axis and T-axis . From this, we can conclude that the relative consistency of microseismic focal mechanism before the strong earthquakes in the source region is a temporary manifestation of the stress concentration of the seismogenic fault under the regional stress field.