Frequency-domain waveform seismic tomography includes modeling of wave propagation and full waveform inversion of correcting the initial velocity model. In the forward modeling, we use direct solution based on sparse ...Frequency-domain waveform seismic tomography includes modeling of wave propagation and full waveform inversion of correcting the initial velocity model. In the forward modeling, we use direct solution based on sparse matrix factorization, combined with nine-point finite-difference for the linear system of equations. In the waveform inversion, we use preconditioned gradient method where the preconditioner is provided by the diagonal of the approximate Hessian matrix. We successfully applied waveform inversion method from low to high frequency in two sets of Marmousi data. One is the data set generated by frequencydomain finite-difference modeling, and the other is the original Marmousi shots data set. The former result is very close to the true velocity model. In the original shots data set inversion, we replace the prior source with estimated source; the result is also acceptable, and consistent with the true model.展开更多
To the most of velocity fields, the traveltimes of the first break that seismic waves propagate along rays can be computed on a 2-D or 3-D numerical grid by finite-difference extrapolation. Under ensuring accuracy, to...To the most of velocity fields, the traveltimes of the first break that seismic waves propagate along rays can be computed on a 2-D or 3-D numerical grid by finite-difference extrapolation. Under ensuring accuracy, to improve calculating efficiency and adaptability, the calculation method of first-arrival traveltime of finite-difference is de- rived based on any rectangular grid and a local plane wavefront approximation. In addition, head waves and scat- tering waves are properly treated and shadow and caustic zones cannot be encountered, which appear in traditional ray-tracing. The testes of two simple models and the complex Marmousi model show that the method has higher accuracy and adaptability to complex structure with strong vertical and lateral velocity variation, and Kirchhoff prestack depth migration based on this method can basically achieve the position imaging effects of wave equation prestack depth migration in major structures and targets. Because of not taking account of the later arrivals energy, the effect of its amplitude preservation is worse than that by wave equation method, but its computing efficiency is higher than that by total Green′s function method and wave equation method.展开更多
波动方程有限差分数值模拟是研究地震波在地下介质中的波场特征和传播机理的重要手段。对于常规有限差分技术,当采用大网格对计算空间进行差分离散时会出现严重的数值频散问题,降低了计算精度。通量校正(Flux-corrected transport metho...波动方程有限差分数值模拟是研究地震波在地下介质中的波场特征和传播机理的重要手段。对于常规有限差分技术,当采用大网格对计算空间进行差分离散时会出现严重的数值频散问题,降低了计算精度。通量校正(Flux-corrected transport method,FCT)技术能够有效压制粗网格情况下有限差分的数值频散。本文研究了具有垂直对称轴横向各向同性(Vertical Transverse Isotropy,VTI)介质的交错网格FCT有限差分技术。首先从一阶速度—应力弹性波方程出发,在交错网格空间中给出了该方程的高阶有限差分法格式及稳定性条件,在此基础上研究了波动方程正演过程中的数值频散FCT压制技术,二者结合实现了该方程的高精度有限差分数值模拟。同常规算法相比,本文算法不额外增加内存需求,少量增加计算量,但可有效压制VTI介质中弹性波动方程正演的数值频散现象。当采用大网格进行数值模拟时,本文方法明显提高了波场模拟精度。展开更多
基金Supported by the National Natural Science Foundation of China (69983005)
文摘Frequency-domain waveform seismic tomography includes modeling of wave propagation and full waveform inversion of correcting the initial velocity model. In the forward modeling, we use direct solution based on sparse matrix factorization, combined with nine-point finite-difference for the linear system of equations. In the waveform inversion, we use preconditioned gradient method where the preconditioner is provided by the diagonal of the approximate Hessian matrix. We successfully applied waveform inversion method from low to high frequency in two sets of Marmousi data. One is the data set generated by frequencydomain finite-difference modeling, and the other is the original Marmousi shots data set. The former result is very close to the true velocity model. In the original shots data set inversion, we replace the prior source with estimated source; the result is also acceptable, and consistent with the true model.
基金National Natural Science Foundation of China (49894190-024) and Geophysical Prospecting Key Laboratory Foun- dation of China National Petroleum Corporation.
文摘To the most of velocity fields, the traveltimes of the first break that seismic waves propagate along rays can be computed on a 2-D or 3-D numerical grid by finite-difference extrapolation. Under ensuring accuracy, to improve calculating efficiency and adaptability, the calculation method of first-arrival traveltime of finite-difference is de- rived based on any rectangular grid and a local plane wavefront approximation. In addition, head waves and scat- tering waves are properly treated and shadow and caustic zones cannot be encountered, which appear in traditional ray-tracing. The testes of two simple models and the complex Marmousi model show that the method has higher accuracy and adaptability to complex structure with strong vertical and lateral velocity variation, and Kirchhoff prestack depth migration based on this method can basically achieve the position imaging effects of wave equation prestack depth migration in major structures and targets. Because of not taking account of the later arrivals energy, the effect of its amplitude preservation is worse than that by wave equation method, but its computing efficiency is higher than that by total Green′s function method and wave equation method.
文摘波动方程有限差分数值模拟是研究地震波在地下介质中的波场特征和传播机理的重要手段。对于常规有限差分技术,当采用大网格对计算空间进行差分离散时会出现严重的数值频散问题,降低了计算精度。通量校正(Flux-corrected transport method,FCT)技术能够有效压制粗网格情况下有限差分的数值频散。本文研究了具有垂直对称轴横向各向同性(Vertical Transverse Isotropy,VTI)介质的交错网格FCT有限差分技术。首先从一阶速度—应力弹性波方程出发,在交错网格空间中给出了该方程的高阶有限差分法格式及稳定性条件,在此基础上研究了波动方程正演过程中的数值频散FCT压制技术,二者结合实现了该方程的高精度有限差分数值模拟。同常规算法相比,本文算法不额外增加内存需求,少量增加计算量,但可有效压制VTI介质中弹性波动方程正演的数值频散现象。当采用大网格进行数值模拟时,本文方法明显提高了波场模拟精度。
文摘逆时偏移成像建立在全波波动方程基础上,偏移成像结果精准,但偏移时计算耗时长,影响了逆时偏移的实际应用.以缩短逆时偏移的计算时间为目的,分析造成计算耗时的原因,采用基于提升构架的整数小波变换的多级树集合分裂(set partitioning in hierarchical tree,SPIH了)图像编码方法降低逆时偏移计算时的内存占有量,解决了计算耗时过长的问题,提高了综合计算效率.对Marmousi模型叠前深度逆时偏移处理表明,该方法能较好地解决逆时偏移计算耗时的问题,而且不影响成像精度.
