张北地震地下流体异常场的研究

Research of the field of subsurface fluid anomalies before the Zhangbei earthquake

对比研究了张北MS6.2和MS5.6地震前地下流体异常时空演化特征。结合二次地震前的地震活动图像及其迁移规律,二次地震所产生的地表宏观裂度与地震的震源机制解,研究结果认为:地下流体趋势异常空间分布受区域构造格局控制;短期异常具有重复性,可能受震源机制影响;短期异常的强度、临震异常形态的差异性以及地震宏观破裂的差异性与地震强度和交替活动的构造有关;MS5.6地震应为MS6.2地震后该地区能量的进一步释放,并且是NE向构造带与近EW向构造带交替活动的结果;二次地震前的短期异常主要沿着近EW向张家口-渤海构造带分布,可能说明近EW向张家口-渤海构造带活动水平高于NE向山西构造带。

The features of subsurface fluid anomalies before Zhangbei earthquakes with MS6.2 and MS5.6 have been comparatively researched. Combining the focal mechanisms and the isoseismal contours of the two events, with the pattern of the small to moderate seismic activity before the two events, some research results are obtained as follows. ① MS5.6 earthquake is a strong aftershock of MS6.2 earthquake, and these two events might be caused by the alternating slip of two intersecting tectonic belts; ② the distribution of longterm subsurface fluid anomalies was controlled by the tectonic belts; ③ the shortterm subsurface anomalies were located along ZhangjiakouBohai tectonic belt trending EW, which might imply that the ZhangjiakouBohai tectonic belt would be more active than the others; ④ the reason that the typical short term anomalies in some stations occurred repeatedly before the two events might be the similar focal mechanisms; ⑤ the difference of the intensity of the short term anomalies and of the isoseismal contours might be caused by difference of the seismic intensity of the two events.