Abstract: Seismic method is a necessary exploration method for detecting active faults buried directly beneath major cities in deep coverage area.Different array length must be adopted for different detecting depth.The Xiadian Fault is a seismogenic fault and related to the 1679 Sanhe-Pinggu earthquake(M=8.0).The deep and moderate-deep structural characteristics of the fault are revealed from the deep and moderate-deep seismic profiles across the fault.To research the activity of the fault away from the earthquake region,moderate-shallow seismic reflection detection experiment was developed with the working parameters as 5m group interval,15m offset,10 folds,60 active receiving channels,single-ended spread shooting by Wacker source,and one point receiving by 40Hz geophones.Based on the results of moderate-shallow seismic detection,a shallow seismic profile was laid across the fault detected by moderate-shallow seismic profiling.The shallow seismic reflection detection experiment was developed by using 2m group interval and hammer source as well as other ways similar to the moderate-shallow seismic reflection.It shows by the results of moderate-shallow and shallow seismic detection that the Xiadian Fault is well imaged at the depth below 200m on the seismic profile of 5m group interval,but it is invisible at the depth above 200m on the profile.The fault on the seismic profile of 2m group interval is obvious,but the shallowest reflection(depth about 30m)on the profile is uninterrupted.It can be educed that the activity of Xiadian Fault weakens about 30km southwest of the epicenter of the 1679 M8.0 Sanhe-Pinggu earthquake.

Key words: Xiadian Fault, seismic reflection, high-resolution, activity at the shallow part

摘要： 地震方法是针对厚覆盖区城市直下型活动断裂的一种不可替代的探测技术,对于不同的探测深度需采用不同的排列长度。为研究夏垫断裂在远离三河-平谷8.0级地震震源区的活动性,我们在该震源区SW方向约30km处开展了中浅层反射地震探测试验,并跨过中浅层地震探测到的夏垫断裂进行了浅层反射地震探测试验。浅层和中浅层地震探测的试验结果表明,在5m道间距的地震剖面上,在200m深度以下夏垫断裂得到了较好的反映,在该深度以上,该断裂反映不明显;在2m道间距的地震剖面上,夏垫断裂错断明显,但剖面上的最浅一组反射波(深度约30m)却没有发生明显错断。由此得出:距1679年三河-平谷8.0级地震震源位置SW方向约30km处,夏垫断裂的活动性减弱。

关键词: 夏垫断裂, 反射地震, 高分辨率, 浅部活动性