论文标题
混合机学习的地震反演
Seismic Inversion by Hybrid Machine Learning
论文作者
论文摘要
我们提出了一种新的地震反演方法,该方法使用深度学习(DL)特征进行地下速度模型估计。 DL功能是高维地震数据的低维表示,该表示由卷积自动编码器(CAE)自动生成并保存在潜在空间中。低维DL功能包含输入地震数据的关键信息。因此,与其直接比较观察到的数据和预测数据之间的波形差异,例如全波倒置(FWI)。我们在CAE的潜在空间中测量其DL特征差异。这种低维比较的优点在于,与FWI相比,它不太容易出现循环滑雪问题。原因是当潜在空间尺寸较小时,DL功能主要包含输入地震数据的运动信息,例如旅行时间。但是,当潜在空间维度变大时,可以保留更多动态信息,例如波形变化。因此,我们提出了一种多尺度反演方法,该方法始于在地下模型的低波动信息中反转低维DL特征。然后,通过颠倒高维DL功能来恢复其高波动细节。但是,没有控制方程包含同一方程式中的速度和DL特征项。因此,我们使用自动分化(AD)将DL特征的扰动连接到速度扰动。用另一个单词,我们通过使用AD将深度学习网络与波动方程式倒置联系起来。我们将这种混合连接表示为混合机器学习(HML)反演。在这里,广告用黑匣子代替了梯度的复杂数学推导,因此任何人都可以在没有深层地球物理背景的情况下进行HML。
We present a new seismic inversion method that uses deep learning (DL) features for the subsurface velocity model estimation. The DL feature is a low-dimensional representation of the high-dimensional seismic data, which is automatically generated by a convolutional autoencoder (CAE) and preserved in the latent space. The low-dimensional DL feature contains the key information of the input seismic data. Therefore, instead of directly comparing the waveform differences between the observed and predicted data, such as full-waveform inversion (FWI). We measure their DL feature differences in the latent space of a CAE. The advantage of this low-dimensional comparison is that it is less prone to the cycle-skipping problem compared to FWI. The reason is that the DL features mainly contain the kinematic information, such as traveltime, of the input seismic data when the latent space dimension is small. However, more dynamic information, such as the waveform variations, can be preserved in the DL feature when the latent space dimension becomes larger. Therefore we propose a multiscale inversion approach that starts with inverting the low-dimensional DL features for the low-wavenumber information of the subsurface model. Then recover its high-wavenumber details through inverting the high-dimensional DL features. However, there is no governing equation that contains both the velocity and DL feature terms in the same equation. Therefore we use the automatic differentiation (AD) to numerically connect the perturbation of DL features to the velocity perturbation. In another word, we connect a deep learning network with the wave-equation inversion by using the AD. We denote this hybrid connection as hybrid machine learning (HML) inversion. Here, the AD replaces the complex math derivations of the gradient with a black box so anyone can do HML without having a deep geophysical background.