【摘要】 波动方程宽角抛物逼近得到的通常是非常系数的单程波传播算子,其系数是速度横向变化的函数,因此需要利用有限差分(FD)进行数值实施.通过对Lippmann-Schwinger单程波动积分方程的退化核逼近,本文研究了一类宽角退化算子的偏移成像.这种退化偏移算子只用快速Fourier变换进行波场延拓,将常规的Fourier分裂步地震偏移方法(SSF)推广适应强速度横向变化介质和大角度传播波场.退化的Fourier偏移算子通过在两个分裂步项之间作波数域线性插值来实现波场延拓,每延拓一层需要比常规的SSF地震偏移方法多一次快速Fourier变换(FFT).通过SEG/EAGE盐丘模型和实际地震资料的应用表明,退化Fourier偏移算子能很好地对盐下的陡倾角断层和实际地震剖面上的复杂小断块和大断裂地质构造成像.更多还原

【Abstract】 Wide-angle parabolic approximations to wave equation usually lead to non-constant differential migrators with their coefficients varying with lateral velocity variations, and hence require a finite-difference numerical implementation. With degenerate approximations to the one-way Lippmann-Schwinger integral equation, we study a category of wide-angle degenerate migrators that permit the implementation of seismic migration using fast Fourier transforms alone. The computationally efficient degenerate migrators extend the split-step Fourier (SSF) method to steeper propagation angles in large-contrast media at the cost of one more Fourier transform for each extrapolation step. Advancing wavefields by the degenerate migrators is actually a linear interpolation between two split-step terms in the wavenumber domain. When applied to image the subsalt dipping faults in the SEG/EAGE salt model and fault blocks/zones in real datasets, the seismic migration by degenerate migrators gives well positioned images for fault-related complex geological structures.更多还原