北京地区中小地震震源机制及构造应力场研究

FOCAL MECHANISMS OF MODERATE AND SMALL EARTHQUAKES AND TECTONIC STRESS FIELD IN THE BEIJING AREA

本文利用简化了的、最大振幅比方法测定中、小地震震源参数的程序,计算了北京及邻区1983—1987年所记录的129个中、小地震的震源机制参数。分析结果表明,大多数中、小地震震源机制的两组节面的走向是互相垂直的;P轴和T轴都近似于水平;P轴大多数分布在北东—南西向,T轴大多数分布在北西—南东向。 结果表明,近几年北京及邻区的区域构造应力场方向较为稳定,未发现该区的平均节面解有显著变化。这说明该区域构造直力场仍处于水平分量占优势的北东向压应力和北西向张应力作用的现代构造应力场中。因此,本方法可作为监视区域构造应力场动态变化的有效方法。

The focal mechanism parameters of 129 moderate and small earthquakes recorded in 1983-1987 in and around Beijing region are computed by means of a simplified maximum-amplitude-ratio of P and S method. The results show that the tendency of two group of nodal planes of focal mechanisms of most moderate and small shocks are perpendicular, the P and T axes are almost horizontal. Most P axes spread NE-SW direction and T axes NW-SE direction, respectively.Results show that in recent years, the regional tectonic stress field in and around Beijing area becomes relatively stable and no obvious variation in average nodal plane solution in this region has been found. This indicates that the regional tectonic stress field in this region is still in modern tectonic stress field affected by NE compress stress and NW tensile stress with the horizontal component prevailing. It can be seen that this is an effective method for monitoring the dynamic state variation of regional tectonic stress field.