【摘要】 采用点源位错模型,层状介质速度结构,通过计算理论地震图,与观测的地震垂直向记录的直达P、S波最大振幅拟合,反演震源机制的方法。系统查阅了万余张地震记录图件,得到可信的小地震震源机制共计554个。有震源机制的地震完全覆盖了序列的震区范围,时间上也分布于序列的各个阶段,因此认为这些小地震对于地震序列具有一定的代表性。计算2个震源机制的2个P轴在三维空间中的夹角和2个T轴之间的夹角,再以2个夹角之和作为距离,采用系统聚类的方法对大量地震震源机制解进行分类。取和主体破裂方向(NE)一致的两类正断层地震,求其占全部类型的地震数目的比例,用来刻画应力场的变动情况。对照伽师序列的6级强震,两类正断层地震出现3次显著的增加。3组强震都在其后发生,这就给出了确切的前兆信息。小地震震源机制显示出的变化,表明它们对于强震孕育发生非常灵敏。文章最后提出伽师强震序列的块体旋转成因模型。更多还原

【Abstract】 Using the dislocation model of the point source and layered velocity structure in crustal medium,through computing the theoretical seismic seismograms,we synthesized the maximum amplitude of P and S wave in vertical components with the observation earthquake in order to inverse the focal mechanism.About ten thousands of earthquake record have been studied,and 554 focal mechanism solutions of credible small earthquakes are obtained.The earthquakes with the focal mechanism solution cover completely the seismic region of the sequence.It has also distributed in all time duration in the sequences.So we think that these small earthquakes can be represented for the whole sequence.We calculate the angles between the P axis and the T axis of two focal mechanism solutions in 3 dimensions,and take the sum of two angles as the distance.By using the system cluster method,the classification of focal mechanism solutions has been carried out.We chose two types of normal fault which is consistent with the main fracture direction(NE).And compute the proportion of earthquake numbers in all types.Then,using it to reflect the change of the stress field.Comparing the type of M6 earthquakes in Jiashi sequence,two types of the normal fault earthquakes occur remarkablely before M6 earthquakes.It seems the change of the focal mechanism of the small earthquake may indicate some precursory meanings.Finally,the model of the block body revolving for the Jiashi strong earthquake sequence has been suggested.更多还原