利用浅层地震反射法探测夏垫断裂浅部特征及空间展布

Shallow structural characteristics and spatial distribution of Xiadian fault by shallow seismic reflection method

为进一步深入研究夏垫断裂的发震构造及活动性,在夏垫断裂震中区开展浅层地震勘探,布设小道距、高密度地震勘探测线,对地震反射剖面进行综合解释。以潘各庄段为中心,向两侧展开布设,共布设浅层地震勘探测线12条,测线总长约18 km。野外数据采集采用中间激发、双边不对称接收、满覆盖次数不少于12次的观测系统。原始资料经过常规处理和精细处理,获得了高质量的反射波叠加时间剖面。地震反射时间剖面揭示的波组变化特征明显,断裂特征清晰,解释夏垫断裂为倾向SE、视倾角约为72°的正断层;同时展现了自小石各庄至南张岱延伸约20 km范围内夏垫断裂的空间展布及浅部构造特征,解释测线范围内夏垫断裂走向约为N40°E。在此基础上,结合微地貌测量和以往研究成果,推测夏垫断裂为全新世活动断裂,其中夏垫断裂中心段伴随次断裂发育和断层绕射波,该特征向两侧减弱,与断裂陡坎的分布和连续的高差变化相对应,同时验证了夏垫镇潘各庄附近为震中的结果。探测结果所揭示的夏垫断裂的空间展布及地层结构特征与地质资料吻合。

In order to further study the seismogenic structure and activity of Xiadian fault,the shallow seismic exploration is carried out in the epicenter of Xiadian fault with the seismic exploration lines of small trace interval and high density;and the seismic reflection profiles are comprehensively interpreted. The seismic exploration lines are laied toward both sides with Pangezhuang as center. There are 12 seismic exploration lines with a total length of about18 km. Field data acquisition geometry is intermediate excitation and bilateral asymmetric reception with no less than 12 full coverages. Through the normal and fine processing,the reflected wave stacking time sections are acquired,revealing the wave group variation characteristics and the clear fracture features. Xiadian fault is interpreted as normal fault with dip SE,apparent dip angle about 72°. Meanwhile,the stacked time sections also show the shallow structural characteristics and distribution of Xiadian fault from Xiaoshigezhuang to Nanzhangdai,about 20 km long. The fault strike is about N40°E in exploration line scope. Therefore,it is inferred that Xiadian fault is a Holocene active fault according to the microtopographic survey and previous research findings. As for the center section of Xiadian fault,secondary fault develop and diffracted waves appear obviously,and weaken toward the two sides,which is coincident with the distribution of fault scarp and continuous elevation changes,verifying that the epicenter was located near Pangezhuang,Xiadian town. The spatial distribution of Xiadian fault and the strata structure features revealed by exploration agree well with geological data.