Elastic wave-equation-based reflection kernel analysis and traveltime inversion using wave mode decomposition
Elastic wave-equation-based reflection kernel analysis and traveltime inversion using wave mode decomposition
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基于弹性波方程的反射核分析和波模分解走时反演
DOI：
10.1093/gji/ggy291
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发表时间：
2018
影响因子：
2.8
通讯作者：
Chenlong Wang
中科院分区：
文献类型：
--
作者：
Tengfei Wang;Jiubing Cheng;Qiang Guo;Chenlong Wang
弹性反射波波形反演（ERWI）利用反射波更新弹性模型深部的低、中波数，可以为弹性全波形反演（EFWI）提供良好的初始模型。虽然ERWI的目的是减轻非线性的反演时，从一个穷人的初始模型，它遭受的周期跳跃问题，由于波形拟合的目标函数。通过弹性波动方程反射走时反演（ERTI）建立EFWI的初始P波和S波速度模型是有效的和鲁棒的，因为走时信息与背景模型更线性地相关。然而，由于S波场的存在，目前在弹性介质中声波走时反演的实现并不简单。波模分解，无论是在记录表面上，并在外推波场，是重要的ERTI。首先，对于P波源地震数据，多分量地震记录的P/S分离分离出了P波和PS波反射同相轴，从而使得通过动态图像变形（DIW）提取这些孤立反射的同相轴间时移成为可能。然后，我们可以使用PP和PS反射的走时残差来建立ERTI的目标函数。其次，基于对弹性介质中复杂反射核的研究，我们证明了对外推的弹性波场进行波模分解的必要性，以抑制由前向和后向传播波场中分量的不期望的互相关引起的伪影。因此，地面记录数据和外推波场的分解保证了在ERTI期间包含旅行时的主要贡献。因此，我们提出了一种两阶段的方法，首先使用分离的PP反射建立P波背景速度，然后使用分离的PS反射建立S波背景速度，基于良好恢复的P波速度模型。Sigsbee 2A模型的数值算例表明了ERTI方法的有效性。
Elastic reflection waveform inversion (ERWI) utilizes reflections to update the low and intermediate wavenumbers in the deeper part of elastic models and can provide good initial models for elastic full waveform inversion (EFWI). Although ERWI aims to mitigate the nonlinearity of inversion when starting from a poor initial model, it suffers from the cycle-skipping problem due to the objective function of waveform fitting. Building initialP- andS-wave velocity models for EFWI through elastic wave-equation reflection traveltime inversion (ERTI) would be effective and robust since traveltime information relates to the background model more linearly. However, the current implementations of acoustic traveltime inversion is not straightforward in elastic media due to the existence ofS-wavefields. Wave mode decomposition, both on the recording surface and in the extrapolated wavefields, is important for ERTI. First, for seismic data withP-wave sources, theP/Sseparation of multicomponent seismograms isolates thePPandPSreflection events and thus make it possible to extract the event-to-event time-shifts of these isolated reflections through dynamic image warping (DIW). Then, we can use the traveltime residuals ofPPandPSreflections to build the objective function for ERTI. Second, based on the investigation of the complicated reflection kernels in an elastic medium, we demonstrate the necessity of wave mode decomposition applied on the extrapolated elastic wavefields, to suppress the artefacts induced by the undesirable cross-correlations of the components in forward and back-propagated wavefields. Therefore, the decomposition of surface recording data and extrapolated wavefields guarantees the dominate contribution of the traveltime is included during the ERTI. Accordingly, we propose a two-stage method to first build theP-wave background velocity using the separatedPPreflections and then build theS-wave background velocity using the separatedPSreflections based on the well-recoveredP-wave velocity model. A numerical example of the Sigsbee2A model shows the effectiveness of the proposed ERTI approach.