Abstract: The investigation and study of fault activities are a basic work for urban earthquake prevention and disasters reduction.In order to find out the location,characteristics and activities of the Laoyachen Fault in Zhengzhou,the high-resolution shallow seismic P and S wave survey profiling across the Laoyachen Fault was carried out at the end of 2006,and different seismic sources along with combinations of diverse observation geometries with different parameters were used.The fine structures in different depths beneath the profile were obtained and the patterns as well as characteristics of the Laoyachen Fault were determined.The results show that the Laoyachen Fault,running in NW and dipping in NE,is a normal fault and its dip angle is about 60°～70°,which incises strata of Eocene,Permian,Carboniferous or Ordovician epoch and goes up to the top boundary of Eocene stratum at the 800～850m depth.There is no any reflector of offset stratum found in Q+N strata.The borehole geological sections across steep slopes of earth surface present that the layers inferred from reflected seismic wave groups of shallow seismic profile are well correspondent with boring geological layers.The borehole results reveal that the three reference laminas,i.e.the boundary between Malan loess and silt with clay soil at about 21m in depth,the calcareous gravel clay layer of 53.9m deep,and the calcareous silt layer of 61.9m deep,all have not depth variations at the two sides of surface steep slopes and are situated almost at the same ground surface elevations,which suggests that the steep slopes at the earth's surface should not result from the activities of Laoyachen Fault.In this study,through shallow seismic P wave and S wave exploration as well as combination of joint borehole geological sections,not only the location and characteristics of Laoyachen Fault was determined,but the geological and seismological evidences for the fault activity estimations were provided.

Key words: Laoyachen Fault, shallow seismic P and S wave exploration, fault activity

摘要： 断层活动性的探测研究是城市防震减灾的基础性工作。为了查明郑州老鸦陈断层的位置、性质及其活动性,2006年底跨老鸦陈断层进行了高分辨率的浅层地震P波和S波探测,通过采用不同的地震波激发源、不同的观测系统参数相结合的工作方法,获得了沿剖面不同深度的地下细结构图像,揭示了老鸦陈断层的形态和特征。结果表明,老鸦陈断层为一条倾向NE、走向NW的正断层,该断层错断了新近系(N)以前的地层,在Q+N地层内部没有发现断层引起的地层错断现象。

关键词: 老鸦陈断层, 浅层地震P波和S波勘探, 断层活动性