起伏地表弹性波传播有限差分法数值模拟
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摘要
有限差分是进行地震波传播数值模拟的最常用方法,但该方法处理起伏的自由边界比较困难。为此,通过对不同地形起伏情况下自由边界的具体分析,将整个二维空间离散点划分为24类,对每一类自由边界处的网格点选择了合理的表现方式,实现了起伏地表自由边界条件的数值化。该方法可以模拟出地表起伏情况下弹性波复杂的传播现象,为进行起伏地表地震波传播规律研究、山地地震勘探野外观测系统设计、山地地震勘探干扰波分析和识别、以及静校正研究提供了正演模拟工具。模拟实例表明,地形起伏引起面波、体波等地震波型之间的相互转化,产生了大量的散射P波、散射S波和散射面波,尤其是由沿地表传播的强能量面波,在地表起伏及近地表物性突变处产生了大量的强能量散射面波,同时也产生了相对较弱的散射P波和散射S波,这是造成山地地震资料信噪比低的主要原因。
The finite difference method is most widely used in the numerical simulation of seismic wave propagation,but is helpless for the fluctuant free boundary.By specifically analyzing the free boundary in different topography relief,the paper classified all the discrete points in 2D computational domain into 24 categories with different finite-difference algorithms,then selected the reasonable representation modes for the gridding points at various free boundaries to realize the numerical procedure of free boundary of rugged topography.This method can simulate the complex elastic wave propagation with rugged topogra-phy,and provide forward modeling tool for the study on seismic wave propagation rule,geometry design,noise analysis and recognition,and static correction in seismic exploration in mountainous regions with rugged topography.The results of numerical modeling examples show inter-conversion of different seismic wave types,such as surface wave and body wave,a lot of scattering P wave,scattering S wave,and scattering surface wave are also generated due to the presence of rugged topography,especially,the ground roll with strong energy will generate strong scattering ground roll and some relative weak scattering P-and S-wave at the locations with rugged topography and the strong variations of the near surface petrophysical properties,which is the main reasons resulting in low S/N data in seismic exploration in mountainous regions.
The finite difference method is most widely used in the numerical simulation of seismic wave propagation,but is helpless for the fluctuant free boundary.By specifically analyzing the free boundary in different topography relief,the paper classified all the discrete points in 2D computational domain into 24 categories with different finite-difference algorithms,then selected the reasonable representation modes for the gridding points at various free boundaries to realize the numerical procedure of free boundary of rugged topography.This method can simulate the complex elastic wave propagation with rugged topogra-phy,and provide forward modeling tool for the study on seismic wave propagation rule,geometry design,noise analysis and recognition,and static correction in seismic exploration in mountainous regions with rugged topography.The results of numerical modeling examples show inter-conversion of different seismic wave types,such as surface wave and body wave,a lot of scattering P wave,scattering S wave,and scattering surface wave are also generated due to the presence of rugged topography,especially,the ground roll with strong energy will generate strong scattering ground roll and some relative weak scattering P-and S-wave at the locations with rugged topography and the strong variations of the near surface petrophysical properties,which is the main reasons resulting in low S/N data in seismic exploration in mountainous regions.
引文
[1]MOCZO.Hybrid modeling of P-SVseismic motion at in-homogeneous viscoelastic topographic structures[J].Bull.Seism.Soc.Am.,1997,87.
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[4]PEDERSEN H A,SANCHEZ-SESMA F J,CAMPILLO M.Three-dimensional scattering by two-dimensional topographies[J].Bull.Seism.Soc.Am.,1994,84(4).
[5]HESTHOLM S O,HUSEBYE E S,RUUD B O.2D fi-nite-difference elastic wave modeling including surface topography[J].Geophysical Prospecting,1994,42.
[6]JI H R S,MCLAUGHLIN K L,DER Z A.Free-bounda-ry conditions of arbitrary topography in a two-dimen-sional explicit finite difference scheme[J].Geophysics,1988,53.
[7]MASAHIKO FUYUKI,YOSHIRO MATSUMOTO.Fi-nite difference analysis of rayleigh wave scattering at a trench[J].Bull.Seism.Soc.Am.,1980,70(6).
[8]董良国.复杂地表条件下地震波传播数值模拟[J].勘探地球物理进展,2005,28(3).
[2]黄自萍,张铭,吴文青,等.弹性波传播数值模拟的区域分裂法[J].地球物理学报,2004,47(6).
[3]BOUCHON M,SCHULTZ C A,TOKSOZ M N.Effect of three-dimensional topography on seismic motion[J].Journal of Geophysical Research,1996,101.
[4]PEDERSEN H A,SANCHEZ-SESMA F J,CAMPILLO M.Three-dimensional scattering by two-dimensional topographies[J].Bull.Seism.Soc.Am.,1994,84(4).
[5]HESTHOLM S O,HUSEBYE E S,RUUD B O.2D fi-nite-difference elastic wave modeling including surface topography[J].Geophysical Prospecting,1994,42.
[6]JI H R S,MCLAUGHLIN K L,DER Z A.Free-bounda-ry conditions of arbitrary topography in a two-dimen-sional explicit finite difference scheme[J].Geophysics,1988,53.
[7]MASAHIKO FUYUKI,YOSHIRO MATSUMOTO.Fi-nite difference analysis of rayleigh wave scattering at a trench[J].Bull.Seism.Soc.Am.,1980,70(6).
[8]董良国.复杂地表条件下地震波传播数值模拟[J].勘探地球物理进展,2005,28(3).
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