2012 年天津宝坻2 次有感地震的力学机制研究

Study on the mechanical process of 2 noticeably felt earthquakes in Baodi County，Tianjin in 2012

摘要:

利用地震仪器烈度分布、地震记录初动极性分布、近场地震序列Sg 震相剪切波分裂特征、震中附近应变仪器记录及深井气氦记录等，综合分析了宝坻地区2012 年MS 4. 0、MS 3. 5两次有感地震。研究发现，这2 次地震震级不大，但孕震过程可能伴有地下介质应力状态的变化，表现出震前半年北东东向加速压缩、北北西向拉张至MS3. 5 地震后该状态转缓的动态过程。2 次地震间隔期间地下积累应力疑似没有得到充分释放，地下微裂隙局部调整使得该地深井观测的稀有气体出现高值，MS 3. 5 地震后微裂隙重新闭合，稀有气体恢复背景值，同时地震剪切波快波方位角恢复到北东东向的背景方向。震中区附近的形变、测震、流体等观测异常有一定的时空对应性。

Abstract:

In terms of the instrument intensity distribution，first impulse orientation of seismic velocity records，Sg shear wave split characteristics of a serial of near-regional earthquakes and records of strain and helium gas in deep holes nearby epicenter，we discuss two noticeably felt earthquakes of MS4． 0 and MS3． 5 in Baodi County in 2012 and reveal some gestation traits of these earthquakes． Although the magnitudes of 2 earthquakes are a little small，some stress changes may appeare in the crust in seismogenic process，in the form of an accelerated NEE orientation pressure and NNW dilation half a year before main earthquake． These states alleviated after MS3． 5． In the time interval between two earthquakes，the regional underground accumulated stress may not be fully released． The state change of local underground micro-cracks led to record more deep rare gas． After MS3． 5 micro-cracks closed again，the polarization azimuth of seismic quick shear wave returned to the NEE direction． In the near epicenter region，the abnormal characteristics of strain record，seismogram and deep hole liquid had a certain consistence of observation in time and space．