对旅行时进行抛物型插值的地震射线追踪方法
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摘要
提出一种对旅行时进行抛物线插值的地震射线追踪方法(简称PTI方法),它比基于旅行时线性插值方法(简称LTI方法)计算结果更准确.PTI和LTI方法都是基于2D网格单元模型,用于计算地震波的旅行时和射线路径.首先介绍了相关方法的一些基本概念.旅行时和射线路径都是在网格边界上进行计算的,因此,射线路径在同一恒速网格内是直线.其计算过程有两步.第一步,计算旅行时,第二步追踪射线路径.然后给出了LTI算法的基本公式.因为在炮点网格内可能存在折射波,文章也相应导出了其公式.最后详细推导了PTI方法的公式.通过模型试算对比说明,用PTI方法较LTI算法更精确、更有效,PTI方法是一种很有发展前途的地震射线追踪算法.
A new seismic ray-tracing method was put forward based on parabolic travel-time interpolation(PTI) method,which is more accurate than the linear travel-time interpolation(LTI) method.Both PTI method and LTI method are used to compute seismic travel-times and ray-paths in a 2D gridded cell model.Firstly,some basic concepts related are introduced.The calculations of travel-times and ray-paths are carried out only on cell boundaries.So,the ray-path is always straight in the same cells with uniform velocity.Two steps are applied in the PTI and LTI method.Step 1 computes travel-times and step 2 traces ray-paths.then,the derivation of LTI'formulas process is described.Because of the presence of refraction wave in shot cell,the formula aiming at shot cell is also derivate.Finally,through the comprehension of above-mentioned works,the PTI method is presented.The calculations are more complex than that of LTI method,but the error is limited.Results of numerical model show that the PTI method can trace ray-paths more accurately and efficiently than LTI method does.
A new seismic ray-tracing method was put forward based on parabolic travel-time interpolation(PTI) method,which is more accurate than the linear travel-time interpolation(LTI) method.Both PTI method and LTI method are used to compute seismic travel-times and ray-paths in a 2D gridded cell model.Firstly,some basic concepts related are introduced.The calculations of travel-times and ray-paths are carried out only on cell boundaries.So,the ray-path is always straight in the same cells with uniform velocity.Two steps are applied in the PTI and LTI method.Step 1 computes travel-times and step 2 traces ray-paths.then,the derivation of LTI'formulas process is described.Because of the presence of refraction wave in shot cell,the formula aiming at shot cell is also derivate.Finally,through the comprehension of above-mentioned works,the PTI method is presented.The calculations are more complex than that of LTI method,but the error is limited.Results of numerical model show that the PTI method can trace ray-paths more accurately and efficiently than LTI method does.
引文
[1]Asawaka E.Seismic ray tracing using linear travel-time inter-polation[J].Geophysical Prospecting,1993,41(1):99~112.
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[3]Vidale J.Finite-difference calculation of travel-times in threedimension[J].Geophysics,1990,55(5):521~526.
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[5]赵改善,郝守玲,等.基于旅行时线性插值的地震射线追踪算法[J].石油物探,1998,37(2):14~24.
[6]许琨,吴律,等.改进Moser法射线追踪地[J].地球物理学进展,1998,13(4):60~66.
[7]张钋,刘洪,等.射线追踪方法的发展现状[J].地球物理学进展,2000,15(1):36~44.
[8]张赛民.跨孔地震层析成像研究[D].长沙:中南大学信息物理工程学院,2003.
[9]秦义龙,张中杰,等.利用单频双程波动方程计算初至走时及其振幅[J].地球物理学报,2005,48(2):423~428.
[10]肖宽怀,孙宇,范明外,等.地震CT技术在大风垭隧道地质病害诊治中的应用[J].地球物理学进展,2004,19(3):678~683.
[2]Vidale J.Finite-difference calculation of travel-times[J].Bul-letin of the Seismological Society of America,1988,78(6):2062~2076.
[3]Vidale J.Finite-difference calculation of travel-times in threedimension[J].Geophysics,1990,55(5):521~526.
[4]Moser T J.Shortest path calculation of seismic rays[J].Geo-physics,1991,56(1):59~67.
[5]赵改善,郝守玲,等.基于旅行时线性插值的地震射线追踪算法[J].石油物探,1998,37(2):14~24.
[6]许琨,吴律,等.改进Moser法射线追踪地[J].地球物理学进展,1998,13(4):60~66.
[7]张钋,刘洪,等.射线追踪方法的发展现状[J].地球物理学进展,2000,15(1):36~44.
[8]张赛民.跨孔地震层析成像研究[D].长沙:中南大学信息物理工程学院,2003.
[9]秦义龙,张中杰,等.利用单频双程波动方程计算初至走时及其振幅[J].地球物理学报,2005,48(2):423~428.
[10]肖宽怀,孙宇,范明外,等.地震CT技术在大风垭隧道地质病害诊治中的应用[J].地球物理学进展,2004,19(3):678~683.
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