夏垫断裂北段浅部构造的高分辨率地震反射勘探研究

夏垫断裂是北京东部的一条活动断裂,研究该断裂的分布、性质、活动状况可以完善和优化城市规划,减小地质灾害的破坏.高分辨率地震反射勘探是调查活动断层的一种重要的地球物理方法,能够得到从深度几十米到几千米的地下构造信息.为探明夏垫断裂北段浅部构造,在北京马坊镇南部布置了一条东西向的高分辨率地震反射勘探测线.采用小道间距,中间激发,可控震源激发的方式,克服了城市地震勘探的不利条件,获得了高信噪比的浅层地震剖面,清晰反映了夏垫断裂在第四系底部基岩附近造成的地层错断,确定了该断裂的位置.地震反射时间剖面揭示,夏垫断裂在测区内是一条高倾角、错断至近第四纪内部的活动断裂.断裂性质为正断层,视倾角较陡,断距由深至浅逐步减小,在地震时间剖商到0.1s上超浅层时,本次地震勘探已经不能分辨断层两侧地层的错动.

The Seismic Reflection Study on High-Resolution Profile of Shallow Structure in North Part of Xiadian Fault

Xiadian fault is an active fault in north of Beijing. The study on the distribution, quality and activity condition of this fault will be helpful to make an optimal city plan and minimize the damage of geologic hazard. High--resolution seismic--reflection profile is an important physical method in identifying active faults from tens of meters to thousand me ters. A high--resolution seismic--reflection profile is carried out in the south of Mafang town in Beijing to verify the shallow structure of north part of Xiadian fault. Despite the unconvincing condition of seismic exploration in urban city, a high signal--to--noise ratio seismic profile is acquired by using small geophone interval, split spread and vibroseis, which clearly reflects the disconnection of bedrock at the bottom of the quaternary and de- terminates the location of the fault. Based on the seismic reflection profile, Xiadian fault is a high dip angle fault which extends to the quaternary in exploration area. Since the fault displacement decreases, the depth becomes smaller, the seismic exploration is unable to distinguish the disconnection of formation near the fault at ultra--shallow depth, less than 0. 1 second in seismic time profile.