河北临城地震序列揭示的一条隐伏断层

2017年9月4日河北临城发生M_L4.4地震,这是邢台地区自2003年以来发生的唯一一次M_L4以上地震。震后大量余震沿条带分布,揭示了一条前人未发现的隐伏断层(根据其经过的地点称之为齐家庄-东双井断裂)。为研究该隐伏断层的几何形状和滑动性质,首先基于河北数字地震台网资料对地震序列进行精定位,利用精定位地震数据拟合发震断层面,计算断层面的走向和倾角,并给出其标准差。然后搜集震中附近历史地震的震源机制解,利用网格搜索法反演区域构造应力场参数,根据构造应力场和断层面的几何形状确定齐家庄-东双井断裂的滑动性质。结果表明,临城M_L4.4地震的发震断层为一条近EW向的隐伏断层,产状为走向约92°,倾角约85°,滑动角约-12°,滑动角标准差约8°,为倾向南的高倾角左旋走滑型断层,延伸深度约10km。区域应力场在齐家庄-东双井断裂上产生的相对剪应力和正应力分别为0.650和0.691,此次地震不是在最大剪应力的断层方位发生,表明该断裂不是现今应力场作用下产生的,而是在复杂的历史地质活动中遗留的,该断裂在现今应力场作用下积累了一定的应力而导致了M_L4.4地震的发生。齐家庄-东双井断裂及其性质的发现为该地区的地质构造和地震孕育环境分析提供了基础。

A Blind Fault Revealed by the Lincheng ML4.4 Earthquake Sequence of Hebei Province

The M_L4.4 earthquake in Lincheng occurred on September 4,2017,which was the only M_L4 or greater earthquake in Xingtai region since 2003. The aftershocks were distributed along a belt,which reveals an unknown blind fault(named as the Qijiazhuang-Dongshuangjing fault after the sites it passed by). In order to study the geometry and slip property of this blind fault,we firstly relocated the earthquake sequence by using the Hebei digital seismic network bulletin and obtained the strike,dip and their standard deviation of the fault plane parameters by applying the accurate positioning earthquakes. Secondly,we collected the focal mechanisms of the historical earthquakes near the epicenter,and inverted the regional stress field using the grid search method,and determined the sliding property of the Qijiazhuang-Dongshuangjing fault. The results showed that the seismogenic fault of the Lincheng M_L4.4 earthquake was a blind fault in East-West direction. The strike,dip and rake is 92°,85ånd -12°,respectively,with the standard deviation of rake about 8°. The fault is in south dip direction,with steep and left-lateral strike-slip up to depth of 10km. The relative shear stress and normal stress on the Qijiazhuang-Dongshuangjing fault was estimated as 0.650 and 0.691,respectively,based on the regional stress field. The orientation of the Qijiazhuang-Dongshuangjing fault is not the maximum shear stress fault,which suggests that the found blind fault is not generated by the contemporary tectonic stress,but is left behand the complex historical geological activity. The stress on the Qijiazhuang-Dongshuangjing fault accumulated to a certain extent and resulted the occurrence of the M_L4.4 earthquake. The finding of the Qijiazhuang-Dongshuangjing fault and its property provides a solid foundation on tectonics and seismogenic analysis in study region.