降低弹性波全波形反演强烈非线性的分步反演策略

A multi-step strategy for mitigating severe nonlinearity in elastic full-waveform inversion

弹性波全波形反演是一种高精度估计地下弹性参数的有效工具,然而其面临的非线性问题比声波更加突出。本文提出一种降低非线性程度的分步反演策略,用于纵、横波速度的高精度重建。首先利用基于包络的弹性波波形反演方法重建纵横波速度的背景模型;然后应用基于时间域正演的频率域弹性波全波形反演方法,利用多尺度策略进一步降低弹性波全波形反演的非线性程度,恢复模型的中、高波数成分。数值实验结果表明,当地震数据中缺少低频和大炮检距成分时,这种分步反演策略对于重建高精度纵、横波速度模型非常有效,对于提高横波速度的反演精度效果尤其明显。

Elastic full-waveform inversion(EFWI)is a powerful tool for estimating high-accuracy subsurface elastic parameters.However the nonlinearity in EFWI is much severer than that in acoustic FWI.We propose a multi-step EFWI strategy to mitigate the nonlinearity for the reconstruction of high-accuracy P-and S-wave velocities.We use envelope-based EFWI as first step to update the long wavelength components of P-and S-wave velocities.Using the envelope-based EFWI's results as initial models,a time-domain modeling based frequency-domain EFWI is used to further reduce nonlinearity and recover short wavelength components of the models with hierarchical multi-scale inversion strategy. The numerical test demonstrates that,when the low frequency and long offset components are not available in seismic data,our multi-step strategy is effective for reconstructing high-accuracy P-and S-wave velocities,especially for S-wave velocity.