地震方法确定活动断裂上断点的影响因素分析
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摘要
中国不少城市位于较厚的第四纪松散沉积物覆盖区,在这些松散层内,发育了许多具有相当规模的隐伏断裂,用地震方法能够探测到它们的存在。但用地震方法探测到的这些隐伏断裂的上断点是否代表了真正意义的断裂上断点?文中在讨论地震记录分辨率的基础上,探讨了影响地震勘探效果的记录信噪比、地质构造条件以及资料处理和解释方法:为提高地震记录的信噪比和分辨率,需要采取相应的技术措施,如在数据采集过程中,使敷设的地震剖面垂直断裂走向,在保证地震记录具有较高信噪比的条件下,采用合适的覆盖次数和小道间距接收的工作方法有助于获取更浅波阻抗界面的反射波;在数据处理和解释的过程中,准确求取反射波的速度,采用一些提高地震记录分辨率和信噪比的处理技术,摒弃一些混波处理手段,有助于改善利用地震方法探测隐伏断裂上断点的效果。而对于没有波阻抗差异的地层界面,包括隐伏断裂已经错断的那些地层界面,地震方法则难以对其进行探测。即使地震方法探测到的不一定是真正意义上的隐伏断层上断点,其结果依然可为今后钻孔剖面位置的布设、钻孔深度的设计以及断层活动性的判定提供科学依据。
Urban areas are mostly covered by thick Quaternary loose sediments in China. Many sizable hidden faults are developed in this loose layer. These hidden faults can be detected by using seismic method. Whether or not the upper offset points of the hidden faults detected by seismic method represent the real upper offset points of the faults?On the basis of the discussion on resolution of seismic records,the influence of S/N ratio of seismic records,the seismo-geological conditions and the data processing and interpretation methods on the seismic exploration results is analyzed in this paper. Study results show that appropriate technical measures are necessary for improving the S/N ratio and resolution of seismic records. For example,seismic profiles shall be laid vertical to fault strike during the data acquisition. Under conditions of guaranteed seismic records with high signal-to-noise ratio,the use of the methods with appropriate fold number and small group interval will help to get reflections from shallower wave impedance interfaces. In the course of seismic data processing and interpretation,it would be helpful to improve the effect of detecting the upper offset point of buried fault by obtaining accurate reflected wave velocity and adopting the processing technology that can enhance resolution and S/N ratio of seismic records as well as abandoning some mixed wave processing methods. It is difficult to detect with seismic method the interfaces in stratum without wave impedance difference,including the interface broken by buried fault. Even though the upper offset point of buried fault detected by seismic method is not necessarily the upper offset point in a real sense,the seismic prospecting result still provides scientific basis for the layout of drill hole profile,design of drilling depth,and the determination of fault activity.
Urban areas are mostly covered by thick Quaternary loose sediments in China. Many sizable hidden faults are developed in this loose layer. These hidden faults can be detected by using seismic method. Whether or not the upper offset points of the hidden faults detected by seismic method represent the real upper offset points of the faults?On the basis of the discussion on resolution of seismic records,the influence of S/N ratio of seismic records,the seismo-geological conditions and the data processing and interpretation methods on the seismic exploration results is analyzed in this paper. Study results show that appropriate technical measures are necessary for improving the S/N ratio and resolution of seismic records. For example,seismic profiles shall be laid vertical to fault strike during the data acquisition. Under conditions of guaranteed seismic records with high signal-to-noise ratio,the use of the methods with appropriate fold number and small group interval will help to get reflections from shallower wave impedance interfaces. In the course of seismic data processing and interpretation,it would be helpful to improve the effect of detecting the upper offset point of buried fault by obtaining accurate reflected wave velocity and adopting the processing technology that can enhance resolution and S/N ratio of seismic records as well as abandoning some mixed wave processing methods. It is difficult to detect with seismic method the interfaces in stratum without wave impedance difference,including the interface broken by buried fault. Even though the upper offset point of buried fault detected by seismic method is not necessarily the upper offset point in a real sense,the seismic prospecting result still provides scientific basis for the layout of drill hole profile,design of drilling depth,and the determination of fault activity.
引文
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高景华,徐明才,荣立新,等.2008.利用地震剖面研究夏垫断裂西南段的活动性[J].地震地质,30(2):497—504.GAO Jing-hua,XU Ming-cai,RONG Li-xin,et al.2008.Activity of the southwest segment of Xiadian Fault investigatedby seismic reflection profiling[J].Seismology and Geology,30(2):497—504(in Chinese).
徐明才,高景华,刘建勋,等.2005.应用于城市活断层调查的地震方法技术[J].中国地震,21(1):17—23.XU Ming-cai,GAO Jing-hua,LIU Jian-xun,et al.2005.Application of the seismic method to detecting active faults[J].Earthquake Research in China,21(1):17—23(in Chinese).
刘保金,柴炽章,酆少英,等.2008.第四纪沉积区断层及其上断点探测的地震方法技术:以银川隐伏活动断层为例[J].地球物理学报,51(5):1475—1483.LIU Bao-jin,CHAI Chi-zhang,FENG Shao-ying,et al.2008.Seismic exploration method for buried fault and its upperbreakpoint in Quaternary sediment area-An example of Yinchuan buried active fault[J].Chinese Journal of Geophysics,51(5):1475—1483(in Chinese).
马文涛,唐文榜,徐锡伟,等.2005.北京黄庄-高丽营隐伏断裂立水桥段浅部活动特征的地震探测[J].物探与化探,29(6):503—505.MA Wen-tao,TANG Wen-bang,XU Xi-wei.et al.2005.Seismic exploration of shallow deformation along Lishuiqiaosection of Huangzhuang-Gaoliying active fault in Beijing urban area[J].Geophysical&Geochemical Exploration,29(6):503—505(in Chinese).
于洋,刘鸿福,常锁亮,等.2011.煤田小断层识别的几个主要影响因素分析[J].中国煤炭地质,23(3):56—60.YU Yang,LIU Hong-fu,CHANG Suo-liang,et al.2011Some main contributing factors in coalfield minor fault identification[J].Coal Geology of China,23(3):56—60(in Chinese).
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