Two mathematical models for combined refraction-diffraction of regular and irregular waves on non-uniform current in water of slowly varying topography are presented in this paper. Model I is derived by wave theory an...Two mathematical models for combined refraction-diffraction of regular and irregular waves on non-uniform current in water of slowly varying topography are presented in this paper. Model I is derived by wave theory and variational principle separately. It has two kinds of expressions including the dissipation term. Model n is based on the energy conservation equation with energy flux through the wave crest lines in orthogonal curvilinear coordinates and the wave kinematic conservation equation. The analysis and comparison and special cases of these two models are also given.展开更多
以往使用的求取地震波初至时间的射线追踪法具有不同程度的缺陷,因而在实际应用中存在一定的局限性。本文提出一种将局部算法与扫描算法相结合的、用有限差分解程函方程求取地震波初至时间的方法。方法中考虑了散射波、首波及透射波的存...以往使用的求取地震波初至时间的射线追踪法具有不同程度的缺陷,因而在实际应用中存在一定的局限性。本文提出一种将局部算法与扫描算法相结合的、用有限差分解程函方程求取地震波初至时间的方法。方法中考虑了散射波、首波及透射波的存在,因而可以适用于较复杂的速度模型。在求出初至时间后,利用互易性原理,能准确地得到射线路径。理论模型的试算表明,该方法计算精度较高,适宜地震偏移、层析成像以及 Green 函数的计算。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
基金This work was financially supported by the Science Foundation of National Education Committee of China
文摘Two mathematical models for combined refraction-diffraction of regular and irregular waves on non-uniform current in water of slowly varying topography are presented in this paper. Model I is derived by wave theory and variational principle separately. It has two kinds of expressions including the dissipation term. Model n is based on the energy conservation equation with energy flux through the wave crest lines in orthogonal curvilinear coordinates and the wave kinematic conservation equation. The analysis and comparison and special cases of these two models are also given.
文摘以往使用的求取地震波初至时间的射线追踪法具有不同程度的缺陷,因而在实际应用中存在一定的局限性。本文提出一种将局部算法与扫描算法相结合的、用有限差分解程函方程求取地震波初至时间的方法。方法中考虑了散射波、首波及透射波的存在,因而可以适用于较复杂的速度模型。在求出初至时间后,利用互易性原理,能准确地得到射线路径。理论模型的试算表明,该方法计算精度较高,适宜地震偏移、层析成像以及 Green 函数的计算。
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.
