关键词: 夏垫断裂, 反射地震, 高分辨率, 浅部活动性

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