背景速度模型在反射和折射波Marchenko聚焦中的作用
The role of the background velocity model for the Marchenko focusing of reflected and refracted waves
AI总结：
本文研究了背景速度模型对Marchenko聚焦精度的影响，通过比较不同模型下的Green函数，发现只有当初始速度模型足够详细时，Marchenko算法才能正确生成折射波。
摘要：
Marchenko算法用于恢复地下由虚拟源激发的波场，这些是包含主波和多次反射波的Green函数。这些算法的要求与传统成像算法相同；它们需要速度模型的估计和记录的反射波。我们研究了使用Marchenko方程检索的Green函数对背景速度模型的依赖性，并探讨了问题："为了实现准确的Marchenko聚焦，我们对速度模型需要了解到什么程度？"我们提出了三种不同的背景速度模型，并比较了使用这些模型检索的Green函数。我们显示，使用Marchenko方程检索的Green函数与精确Green函数的相关系数平均大于90%，除了接收器孔径边缘附近。我们还检查了检索的Green函数中是否存在折射波。我们通过数值示例表明，Marchenko聚焦算法仅在迭代方案中使用的初始速度模型足够详细以建模折射波时，才会产生折射波。
英文摘要：
Marchenko algorithms retrieve the wavefields excited by virtual sources in the subsurface, these are the Green's functions consisting of the primary and multiple reflected waves. The requirements for these algorithms are the same as for conventional imaging algorithms; they need an estimate of the velocity model and the recorded reflected waves. We investigate the dependence of the retrieved Green's functions using the Marchenko equation on the background velocity model and address the question: ``How well do we need to know the velocity model for accurate Marchenko focusing?". We present three different background velocity models and compare the Green's functions retrieved using these models. We show that these retrieved Green's functions using the Marchenko equation give correlation coefficients with the exact Green's function larger than 90% on average except near the edges of the receiver aperture. We also examine the presence of refracted waves in the retrieved Green's function. We show with a numerical example that the Marchenko focusing algorithm produces refracted waves only if the initial velocity model used for the iterative scheme is sufficiently detailed to model the refracted waves.
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