采用点源位错模型、层状介质速度结构,利用地震波垂直向记录的直达(P)、(S)波最大振幅,计算小地震震源机制.通过系统聚类,利用矢量合成方法,计算得到各类解的平均震源机制解.采用上述方法,针对2003年以来新疆北天山西段和中天山地区4次中强地震前,震源区周围中小地震震源断错性质和P轴方位的变化进行分析.结果显示,中强地震前2～3年中小地震震源机制解类型随机分布,震前1年表现出明显的优势分布特点,主压应力P轴方位发生较明显的偏转变化.%With maximum amplitude of direct , recorded by the vertical direction, the article applied the point-source dislocation model and layer medium velocity structure to calculate focal mechanism solutions of small earthquakes. With the vector resultant and hierarchial clustering method, we got mean focal mechanism solutions of different classification. With above method, we analyzed the source dislocation character and P axis azimuth of moderate and small earthquakes around the hypo-central region before 4 mid-strong earthquakes in the central Tianshan area in Xinjiang since 2003. The result shows that focal mechanism solution type of small earthquakes in 2 ~ 3 years before these mid-strong earthquakes is stochastic, and the type appears preponderant one year before these mid-strong earthquakes and P axis azimuth exists obvious deflection change.
展开▼
