夏垫断裂带深部构造特征与第四纪活动性讨论

DEEP STRUCTURE AND QUATERNARY ACTIVITIES OF THE XIADIAN FAULT ZONE

利用重力、浅层地震和高密度电阻率法物探工作成果，由深及浅垂向上“接力拼接”的方式，结合钻探等手段，把夏垫断裂带分解为基岩断裂带和第四纪断裂带2个部分进行研究，结果表明：1）夏垫断裂带的基岩断裂带由主干断裂和次级断裂构成。其北段（马坊-西集-带）较窄，南2条主干断裂构成。其南段（西集-凤河营-带）较宽，由3条主干断裂构成。2）第四纪断裂带是基岩断裂带向上延伸的部分，是断裂带最新活动的直观表现，并受控于基岩断裂带。夏垫第四纪断裂带同样由主干和次级断裂构成，北段（马坊-西集-带）由2条主干断裂和分布于北端尾部次级断裂构成，与基岩断裂带-对应关系较好。2条主干断裂产状差异较大，最新活动时间均为全新世。而南段（西集-凤河营-带）断裂分布不连续，很难分清主次断裂，同基岩断裂带的对应关系较差，推测为基岩断裂中夏垫断裂的活动。这些主、次级断裂产状均较为陡立，最新活动时间为晚更新世晚期一全新世早期。3）夏垫断裂带内上、下两盘全新世沉积底界垂向累积位错量为1．7～4．8m，晚、中、早更新世以来则分别为6～26m、26～167m和44～330m，其中最大累积位错量位于夏垫地区，向南、北逐渐减小。4）以张家湾断裂为界把夏垫断裂带划分为南、北2段。北段第四纪活动性强，中强震及微小地震时有发生，而南段第四纪活动性弱，仅发生微小地震。

Xiadian Fault zone is a NNE-trending lithospheric-scale regional deep fault in the eastern part of the capital, also an active fault zone with strong earthquake activities in the history. According to the results of gravity,shallow seismic and high-density electrical geophysical prospecting, by ＂relay stitc- hing＂ vertically from the deep to the shallow ,and in combination with the methods of drilling and oth- er means,the Xiadian Fault zone is studied by dividing it into two parts： the bedrock fault zone and the Quaternary fault zone, and new insights are gained on the characteristics of deep structure and ac- tivity of the Xiadian Fault zone. The results show that ： （ 1 ） the bedrock fault zone of Xiadian Fault consists of main faults and secondary faults. Its northern part, the Mafang-Xiji area, is composed of two major faults with a narrower width, and the southern part, the Xiji-Fengheying area, is composed of three major faults,with a wider width; （2）The Quaternary fault zone of Xiadian Fault is the upward extension of the bedrock fault zone,which is the visual representation of the latest activity of the fault zone and controlled by the bedrock fault zone. The Quaternary fault zone is also composed of main faults and secondary faults. The northern part（Mafang-Xiji area） consists of two major faults and sec- ondary faults distributed in the northern end,corresponding well with the bedrock fault zone. Occur- rence of the two major faults is quite different, and the latest movement of the faults is both in Hol- ocene. While, the southern part of the fault zone（ the Xiji-Fengheying area）is quite discontinuous and is difficult to distinguish between the major and secondary faults. The faults have poor correspondence to the bedrock ones and are inferred to be related with the segmentation of faulting of the bedrock faults. Both major and secondary faults are steep and the date of their latest movement is late Pleisto- cene-early Holocene; （3）The amount of vertical dislocation of the bottom boundary of the Holocene sediments in the hanging and foot walls of Xiadian Fault zone is 1.7 -4.8m,and that of late, middle and early Pleistocene are 6 -26m,26 - 167m and 44 ~ 330m, respectively. The vertical dislocation on the whole fault zone differs greatly,with the highest in the Xiadian area, and decreasing gradually to the south and north ends ; （4） Considering the spatial distribution, structure, occurrence, activity and characteristics of seismic activity along of the fault zone, the Xiadian Fault zone is divided into the southern and northern segments with the Zhangjiawan Fault as the boundary. The northern part expe- rienced intensive Quaternary activity, with frequent moderate and small earthquakes. Quaternary activ- ity is weak along the southern part,where only small earthquakes occurred.