肃南5.7级地震序列震源机制研究及其前兆意义

用Ｐ、Ｓ波振幅比方法反演了１９８８年１１月２２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

STUDY ON THE MECHANISMS OF THE SEISMIC SEQUENCE OF SUNAN EARTHQUAKE(M5.7) AND ITS SIGNIFICANCE TO THE PRECURSOR

The source mechanisms of the seismic sequence of Sunan earthquake(Nov.22,1988,M5.7)have been inverted by using the method of the ratio of P wave and S wave amplitudes,the corresponding P and T axes calculated.The results show that the group of nodal planes of pre shocks puts together comparably and identical with the fault of main shock,so do their P axes.The solutions of nodal plane of the after shocks(and the micro events occurred in the area after the main shock)have comparable scattering distribution but keep identical roughly with the seismic fault,but the P and T axes of after shocks show more scattering distribution.According to the results it is considered that the relative identity of the mechanisms of the micro earthquakes in the source area before a moderate earthquake is a short term precursor,it is because of the stress concentration in the seismic fault under the local stress field.