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首页> 外文期刊>Pure and Applied Geophysics >Up/Down Image Separation in Elastic Reverse Time Migration
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Up/Down Image Separation in Elastic Reverse Time Migration

机译：弹性相反时间迁移中的上/下图像分离

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Reverse time migration (RTM) using a two-way wave equation is able to generate high-quality images of the subsurface. Besides the ability to image complicated geological features, image artifacts can be observed in elastic P and S wave images, where high velocity contrasts/gradients in the velocity model produce back-scattering reflections during wavefield extrapolations. Separating RTM images into components based on wavefield propagation directions is able to effectively remove such image artifacts. We first compare image separation methods, including up/down image separation during, and post, imaging. The post-imaging method is easy to implement using existing RTM software, as it requires only simple operations applied to the stacked RTM images. The separated up/down images are similar to those separated during imaging, but there are also differences. The differences come from the different physical meanings of the up/down separated images. The during-imaging methods separate RTM image into its up/down components using propagation directions of the individual source/receiver wavefields, while the post-imaging method separates images based on the vector sum of the source and receiver wavefield directions. Inspired by these differences, we develop a composite workflow that combines a cost-efficient up/down imaging condition and a post-imaging separation step, which provides an alternative solution for obtaining up/down separated images from full waveform imaging. Numerical example using an elastic version of the Sigsbee 2A model indicates that the up/down separated images from the proposed workflow are effectively equivalent to those obtained using the during-imaging separation methods. More interestingly, we show the pros and cons in the imaging results from different up/down separation methods, especially in converted P-S images.
机译：使用双向波动方程的反向时间迁移（RTM）能够生成地下的高质量图像。除了能够图像复杂地质特征的能力之外，可以在弹性P和S波图像中观察到图像伪像，其中速度模型中的高速对比/梯度在波场外推期间产生背散射反射。将RTM图像分离为基于波场传播方向的组件能够有效地去除这种图像伪像。我们首先比较图像分离方法，包括期间和发布，成像的上/下的图像分离。使用现有RTM软件易于实现后成像方法，因为它只需要应用于堆叠的RTM图像的简单操作。分离的向上/向下图像类似于成像期间分离的图像，但也存在差异。差异来自上/下分离图像的不同物理含义。在成像方法中使用各个源/接收器波场的传播方向将RTM图像分离到其上/下组件中，而后成像方法基于源和接收器波场方向的矢量和分离图像。灵感来自这些差异，我们开发了一种复合工作流，该复合工作流结合了成本效益的上/下成像条件和后成像分离步骤，其提供了用于从全波形成像获得上/下分离图像的替代解决方案。使用Sigsbee 2a模型的弹性版本的数值示例表示来自所提出的工作流程的上/下分离图像有效地等同于使用期间的成像分离方法获得的图像。更有意义地，我们在成像结果中显示了来自不同上/下分离方法的成像结果，尤其是在转换后的P-S图像中的应用程序。

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