地震勘探中相控阵震源的方向特性研究
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摘要
电磁驱动式可控震源在城市浅层地震勘探中所面临的最突出的困难是微弱的反射信号常常淹没在很强的背景噪声之中.为了提高地震记录的信噪比,可以利用多台可控震源阵列实施相位控制形成定向地震波束以增强地震波的能量.本文讨论这种相控阵震源的波束形成机制.引入了地震波场的边际能量密度的概念,利用地震波场的时间切片技术,对模型空间各个方向上的能量强度进行了定量分析.用有限差分法对相控阵震源Chirp信号扫描的地震响应进行了数值模拟.当定向地震波束的汇聚带与观测排列的空间范围相一致时,相控阵震源合成地震记录的能量强度要显著高于单个可控震源情形的能量强度,波形振幅的均匀性要明显优于常规组合激发震源情形波形振幅的均匀性.
The extrusive difficulty in urban shallow strata seismic exploration with vibrators driven by electro-magnetic force is that the weak reflective seismic signals are often flooded in strong noise background.For increasing signalnoise ratio of seismic records,one can make use of vibrator arrays by phase controlling to concentrate seismic waves into a directed beam so as to enhance the energy of seismic waves.We discuss the mechanism of wave beam forming for the phase array vibrators,give a definition of the marginal energy density for the seismic wave field,and make some quantitative analyses to the energy intensity along each direction on the snapshot of the wave field.Then the finite difference method is used to simulate the response to the Chirp signals produced by the phase array vibrators.When the concentration zone of the directed seismic beam is coincident with the range of the geophone arrangement,the energy intensity of the synthetic seismogram with the phase array vibrators is obviously higher than that with a single vibrator,and the uniformity of the amplitude of seismic wave for the phase array vibrators is obviously better than that for a set of vibrators sprung at the same time.
The extrusive difficulty in urban shallow strata seismic exploration with vibrators driven by electro-magnetic force is that the weak reflective seismic signals are often flooded in strong noise background.For increasing signalnoise ratio of seismic records,one can make use of vibrator arrays by phase controlling to concentrate seismic waves into a directed beam so as to enhance the energy of seismic waves.We discuss the mechanism of wave beam forming for the phase array vibrators,give a definition of the marginal energy density for the seismic wave field,and make some quantitative analyses to the energy intensity along each direction on the snapshot of the wave field.Then the finite difference method is used to simulate the response to the Chirp signals produced by the phase array vibrators.When the concentration zone of the directed seismic beam is coincident with the range of the geophone arrangement,the energy intensity of the synthetic seismogram with the phase array vibrators is obviously higher than that with a single vibrator,and the uniformity of the amplitude of seismic wave for the phase array vibrators is obviously better than that for a set of vibrators sprung at the same time.
引文
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[2]Crawford J M,Doty W E N,Lee M R.Continuous signalseismograph.Geophysics,1960,25(1):95~105
[3]Chapman W L,Brown G L,Fair D W.The vibroseis system:Ahigh-frequency tool.Geophysics,1981,46(12):1657~1666
[4]Lin J.Development of high-resolution geophysical instrumentation forengineering and environmental investigations.International Workshopon High-Resolution Geophysics.Tucson,USA,1997
[5]Lin J.Geophysical instrumentation in China:A review of highereducation and research.The Leading Edge,1997,16(7):30~33
[6]Chen Z B,Lin J.Design for vibrator field experiment based onvibrator-earth system.Journal of Geoscientific Research in NortheastAsia,2000,3(1):107~113
[7]Garrod A.Digital modules for phase array radar.IEEE InternationalRadar Conference.1995.726~731
[8]Arnold M E.Beam forming with vibrator arrays.Geophysics,1977,42(7):1321~1338
[9]孙卫涛,杨慧珠.各向异性介质弹性波传播的三维不规则网格有限差分法.地球物理学报,2004,47(2):332~337Sun W T,Yang H Z.A 3-D finite difference method using irregulargrids for elastic wave propagation in anisotropic media.Chinese J.Geophys.(in Chinese),2004,47(2):332~337
[10]杨顶辉.双相各向异性介质中弹性波方程的有限元解法及波场模拟.地球物理学报,2002,45(4):575~583Yang D H.Finite element method of the elastic wave equation andwavefield simulation in two-phase anisotropic media.Chinese J.Geophys.(in Chinese),2002,45(4):575~583
[11]Zhang J F.Elastic wave modeling in heterogeneous media with highvelocity contrasts.Geophysical Journal International,2004,159(1):223~239
[12]王德利,何樵登,韩立国.裂隙型单斜介质中多方位地面三分量记录模拟.地球物理学报,2005,48(2):386~393Wang D L,He Q D,Han L G.Multi-azimuth three-componentsurface seismic modeling for cracked monoclinic media.Chinese J.Geophys.(in Chinese),2005,48(2):386~393
[13]郑海山,张中杰.横向各向同性(VTI)介质中非线性地震波场模拟.地球物理学报,2005,48(3):660~671Zheng H S,Zhang Z J.Synthetic seismograms of nonlinear seismicwaves in anisotropic(VTI)media.Chinese J.Geophys.(inChinese),2005,48(3):660~671
[14]Yang D H,Wang S Q,Zhang Z J,et al.n-Times absorbingboundary conditions for compact finite-difference modeling of acousticand elastic wave propagation in the 2D TI medium.Bulletin of theSeismological Society ofAmerica,2003,93(6):2389~2401
[15]Carcione J M.Seismic modeling in viscoelastic media.Geophysics,1993,58(1):110~120
[16]Fu L Y,Wu R S.Infinite boundary element absorbing boundary forwave propagation simulations.Geophysics,2000,65(2):596~602
[17]黄自萍,张铭,吴文青等.弹性波传播数值模拟的区域分裂法.地球物理学报,2004,47(6):1094~1100Huang Z P,Zhang M,Wu W Q,et al.A domain decompositionmethod for numerical simulation of the elastic wave propagation.Chinese J.Geophys.(in Chinese),2004,47(6):1094~1100
[18]Komatisch D,Vilotte J P.The spectral element method:an efficienttool to simulate the seismic response of 2D and 3D geologicalstructures.Bull.Seism.Soc.Am.,1998,88:368~392
[19]Engquist B,Majda A.Absorbing boundary conditions for thenumerical simulation of waves.Mathematics of the Computation,1977,31(139):629~651
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