张家口地区近年中小地震震源机制解及应力场反演

Focal Mechanism Solutions and Stress Field Inversion of Recent Medium-small Eearthquakes in Zhangjiakou Area

利用垂直向Pg和Sg波最大振幅比方法,计算得到张家口地区2007—2015年发生的中小地震震源机制解;通过系统聚类分析,研究震源机制分布特征与断裂活动的关系,并采用网格搜索法对张家口地区的现今地壳应力场进行反演,得到了较为精确的张家口地区的构造应力场。结果表明:主压应力轴的走向范围:211°～223°,即NE—SW向;主张应力轴的走向范围:323°～332°,即NNW—SSE向,P轴、T轴都近于水平;两组节面的走向分别为N18°E向和近EW向(N83°E),破裂以水平走滑为主。

Based on the maximum amplitude ratio of vertical Pg and Sg waves,the focal mechanism solutions of medium-small earthquakes in Zhangjiakou area from 2007 to 2015are obtained.According to systematic cluster analysis,the relationship between distribution characteristics of the focal mechanism and fault activity is discussed.In addition,grid search method is employed for inversing the crustal stress field in the Zhangjiakou area.Ultimately,the tectonic stress field in Zhangjiakou area is obtained accurately.The results show that the strike of the principal compressive stress is NE-SW,and ranges from 211to223 degrees.The strike of the principal tensional stress is NNW-SSE with a range of 323~232degrees,which indicates P and T axes are nearly horizontal.The joint strikes of the two groups are N18°E and N83°E respectively.The break mode is dominated by horizontal strike slip.