利用多个震源机制解求祁连山西段平均应力场方向

Determination of the Direction of the Mean Stress Field in the Western Qilian Mountains through Focal Mechanism Solution Analysis

祁连山西段由于受到多个构造块体的共同约束,表现出复杂的地球物理特性和地质特性。本文利用14个中强地震震源机制解和2001-2012年66个中小地震震源机制解分析了区域应力场特征。结果显示,地震的震源性质以走滑和逆冲为主,印证了祁连山西段基本构造变形特征;三个区域应力张量的定量结果显示,最大主压应力σ1方向在NE向,水平挤压作用明显,且具有一定的分区特征,表明局部应力场受到局部构造的影响。

The western segment of the Qilian Mountains,which is controlled by some tectonic blocks,has complicated geography and geology.This study looked at 14 strong-moderate earthquakes and 66 small-moderate earthquakes from 2001 to 2012,used the stress tensor averaging method to calculate the direction of the mean stress axis in the area,and then analyzed the characteristics of the stress field.Moreover,we compared the results with another inversion result by using the FMSI inversion process.Finally,we conducted a detailed study of the tectonic stress field characteristics of the western segment of the Qilian Mountains. With the stress tensor calculation method,we obtained the average direction of T,B,and P axes by calculating the average stress tensor of focal mechanism solutions from multiple earthquakes.If the earthquake has a relatively independent discrete distribution in the block,we can deduce the direction of the principal stress axes in the regional tectonic stress field on the basis of the average direction of T,B,and P axes. In our research,we selected two groups of data,strong-moderate earthquakes and small-moderate earthquakes from 2001 to 2012.We obtained 14 focal mechanism solutions for strong-moderate earthquakes occurring since 1900,with 4 above MS6.0 and 10 between MS5.0 and MS5.9.Furthermore,another was the earthquake that occurred on December 25,1932,the large Changma MS7.6 in the western Changma fault.In addition,we used the CAP method and the vertical P-wave and S-wave amplitude ratio method to calculate the focal mechanisms of small-moderate earthquakes. The focal mechanisms show that the characteristics of focus are mainly strike-slip and thrust earthquakes.The quantification results for stress tensor in three regions show that the azimuth of maximum principal compressive stress,σ1,is NE,and the horizontally compressed acts show evidence of definite subarea characteristics.