1997～1998年伽师强震群小地震震源机制解系统聚类分析

用P、S波最大振幅比法计算1997~1998年伽师强震群MS2.5~3.7小地震震源机制解,对小地震震源机制解进行系统聚类分析。结果表明,伽师小地震主要以走滑和正断层为主,与该时段发生的伽师6级强震具有相似的断错性质。1997年伽师小地震主压应力P轴方位为北东或近南北向,与1997~1998年6级强震主压应力P轴方位一致。1997年4月6日6.4级和1998年8月2日6.1级两次6级正断层地震前出现地震空段现象。

THE SYSTEM CLUSTER ANALYSIS OF THE FOCAL MECHANISM SOLUTIONS ABOUT SMALL EARTHQUAKES IN JIASHI STRONG EARTHQUAKE SWARM FROM 1997 TO 1998

Using the method of the maximum amplitude ratio P/S to calculate the focal mechanisrn solutions of small earthquakes with Ms2.5 -- 3.7 in Jiashi strong earthquake swarm from 1997 to 1998. By the system cluster analysis of the focal mechanism solutions of these small earthquakes, the result showed that small earthquakes of Jiashi are mainly by strike-slip and normal dip-slip fault. They are similar fault with strong earthquakes with Ms6 at the same time in Jiashi swarm. The P axis of the principle compression stress for small earthquakes in 1997 is oriented mainly to NE or nearly NS. And it is consistent with the strong earthquakes with Ms6 from 1997 to 1998. And there appears some phenomena of empty segment before the two earthquakes belong to normal dip-slip fault with Ms6.4 in April 6,1997 and with Ms6.1 in August 2, 1998.