刘玉柱^1,2,
刘伟刚²,
吴世林²,
郑文怡^2,3
1. 同济大学海洋地质国家重点实验室, 上海 200092
2. 同济大学海洋与地球科学学院, 上海 200092
3. 中交上海航道勘察设计研究院有限公司, 上海 200120

基金项目: 国家重点研发计划项目（2018YFC0310100，2019YFC0312004），中国科学院战略性先导科技专项（XDA14010203），国家科技重大专项（2017ZX05005-004）与国家自然科学基金（41930105，41774122，41630964）共同资助


详细信息 中图分类号: P631;P315

收稿日期:2020-02-11
修回日期:2020-05-25
上线日期:2020-08-05

Full waveform inversion based on the spectral element method and its application to OBS data

LIU YuZhu^1,2,
LIU WeiGang²,
WU ShiLin²,
ZHENG WenYi^2,3
1. State Key Laboratory of Marine Geology, Tongji University, Shanghai 200092, China
2. School of Ocean and Earth Science, Tongji University, Shanghai 200092, China
3. Shanghai Waterway Engineering Co., Ltd., Shanghai 200120, China


MSC: P631;P315

--> Received Date: 11 February 2020
Revised Date: 25 May 2020
Available Online: 05 August 2020


摘要
摘要:全波形反演已被广泛应用于获取地下速度结构.而反演问题与正演方法密切联系，针对特定反演问题，合适的正演方法能极大提高反演效率和精度.本文首先验证谱元法在含起伏界面模型数值模拟方面的优势，在此基础上将谱元法作为正演引擎应用于全波形反演，并为克服未知子波的影响，采用一种归一化的频率域目标泛函.结果表明，起伏地表情况下，基于谱元法的全波形反演相比于基于传统有限差分法反演，具有更高的反演精度.进一步，本文将基于谱元法的波形反演方法应用于OBS观测系统的理论合成数据和野外采集数据.谱元法非结构化网格剖分自然满足自由边界条件，能很好地适应不规则海床并模拟多次波.理论实验表明，即使在OBS观测系统很稀疏的情况下，基于谱元法的全波形反演仍能获得海底以下正确的高波数速度结构.在处理实际OBS数据时，本文采用分频策略以减少反演非线性，初始模型成功更新，其结果揭示了西沙海槽海底以下更多的细节信息.
关键词: 全波形反演/
谱元法/
有限差分法/
海底地震仪/
散射积分算法

Abstract:Full waveform inversion (FWI) is a commonly used method to obtain subsurface velocity structures. However, because the inverse problem is closely related to its forward counterparts, choosing an appropriate simulation method for seismic wave propagation for a specific target can improve the inversion efficiency and accuracy. Therefore, the effectiveness of spectral element method is firstly proved. Then, SEM is applied to an acoustic FWI. To suppress the influence of the unknown wavelet, a normalized objective function in frequency domain is used. Experiments reveal that the proposed SEM-based FWI generates results with higher accuracy and better resolution compared to conventional FDM-based approaches, given the presence of topography. In the final part, the SEM-based FWI is applied to a synthetic ocean-bottom-station (OBS) dataset and a field OBS dataset, respectively. SEM is used to fit the irregular seabed and simulate multiples. Synthetic test proves that the SEM-based FWI can still obtain reasonable high-wavenumber velocities under the seafloor even receivers are quite sparse. To further decrease the nonlinearity in FWI for the field OBS dataset, a multi-scale strategy is adopted. Finally, the starting model is successfully updated, and more details are revealed under the Xisha trough.
Key words:Full waveform inversion/
Spectral element method/
Finite difference method/
OBS/
Scattering-integral algorithm



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