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arXiv 1909.11536physics.geo-phphysics.comp-ph
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利用深度学习进行外推全波形反演

Extrapolated full waveform inversion with deep learning

Hongyu Sun, Laurent Demanet

摘要:

由于固有的周期跳跃问题,低频信息和良好的初始模型的缺乏会严重影响全波形反演(FWI)的成功。计算低频外推法原则上是解决这一问题的最直接方法。通过将带宽扩展视为机器学习中的回归问题,我们提出了一种卷积神经网络(CNN)架构,可以自动外推丢失的低频,而无需预处理和后处理步骤。带限记录是CNN的输入,在我们的数值实验中,从足够的样本训练的神经网络可以预测一个合理的近似地震图在未观察到的低频带,无论是在相位和振幅。考虑的数值实验上模拟的P波数据。在外推FWI(EFWI)中,在对带限数据进行频率扫描之前,从外推低频确定模型的低波数分量。所提出的低频外推深度学习方法对于EFWI的初始化步骤具有足够的泛化能力。数值算例表明,在Marmousi模型的几个子模型上训练的神经网络能够预测BP 2004基准模型的低频。此外,神经网络可以鲁棒地处理地震资料的不确定性,由于噪声的存在,已知的震源子波,不同的有限差分格式的正演算子。最后,这种方法不受其他方法的带宽扩展的结构限制,似乎提供了一个诱人的解决方案,正确初始化FWI的问题。

英文摘要:

The lack of low frequency information and a good initial model can seriously affect the success of full waveform inversion (FWI), due to the inherent cycle skipping problem. Computational low frequency extrapolation is in principle the most direct way to address this issue. By considering bandwidth extension as a regression problem in machine learning, we propose an architecture of convolutional neural network (CNN) to automatically extrapolate the missing low frequencies without preprocessing and post-processing steps. The bandlimited recordings are the inputs of the CNN and, in our numerical experiments, a neural network trained from enough samples can predict a reasonable approximation to the seismograms in the unobserved low frequency band, both in phase and in amplitude. The numerical experiments considered are set up on simulated P-wave data. In extrapolated FWI (EFWI), the low-wavenumber components of the model are determined from the extrapolated low frequencies, before proceeding with a frequency sweep of the bandlimited data. The proposed deep-learning method of low-frequency extrapolation shows adequate generalizability for the initialization step of EFWI. Numerical examples show that the neural network trained on several submodels of the Marmousi model is able to predict the low frequencies for the BP 2004 benchmark model. Additionally, the neural network can robustly process seismic data with uncertainties due to the existence of noise, poorly-known source wavelet, and different finite-difference scheme in the forward modeling operator. Finally, this approach is not subject to the structural limitations of other methods for bandwidth extension, and seems to offer a tantalizing solution to the problem of properly initializing FWI.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

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