Abstract: Shallow seismic exploration is the main technique in present urban active faults detecting.The detection precision is not only affected by the factors of sources and receivers,but also closely related to the precision of seismic data processing.Velocity analysis is an important step in seismic data processing,which determines the precision of NMO,CDP stack,post-stack migration and time-depth conversion.Considering the properties of low stack folds,shallow objected layers and big background noise of shallow seismic data,the parameters selection for velocity analysis is studied in the paper.Firstly,by analyzing the offsets of different traces in adjacent CDP gathers,and comparing between single and multiple CDP gathers,the principle of how to extract large CDP gathers is proposed.And then,through comparing the velocity spectra derived from different large CDP gathers,velocity scanning interval,time window length,cutting ratio of NMO,etc.,some effective advices on parameters selection for velocity analysis are given,and meanwhile,several noticeable problems in velocity analysis and time-depth conversion are discussed.

Key words: active fault, shallow seismic exploration, data processing, velocity analysis, parameter selection

摘要： 浅层人工地震勘探是当前城市地震活断层探测的主要方法,勘探精度不仅受激发、接收等因素的影响,还与地震数据处理的精度密切相关.速度分析是地震勘探资料处理中的关键环节,它的准确与否对动校正、共深度点叠加、叠后偏移及时深转换等都将产生影响.针对浅层地震资料目的层较浅、叠加次数少和城市背景干扰大等特点,文中对速度分析的参数选取问题进行了研究.首先通过对相邻CDP道集内各接收道炮检距的分析,以及单个和多个CDP道集的对比,提出了用于速度分析的CDP大道集的抽取原则.并通过对不同的CDP大道集、速度扫描间隔、计算时窗长度、动校切除比例等所获得的速度谱的对比分析,对速度谱扫描过程中各参数的选取提出了建议,并对速度分析及时深转换过程中值得注意的问题进行了讨论.

关键词: 活断层, 浅层地震勘探, 数据处理, 速度分析, 参数选取