A progressive data assimilation strategy in full-waveform adjoint tomography

Abstract

Elastic full-waveform inversion (FWI) is powerful in resolving fine-scale structures in complex models, but suffering from strong nonlinearity and slow convergence rate, especially in the presence of cycle-skipping issues when the initial model is not well constrained. We present a progressive data assimilation (PDA) strategy to mitigate the cycle-skipping issue and boost the convergence rate. Specifically, we split each seismogram into several time windows with a constant length after the first arrival. At each iteration, the PDA strategy automatically screens the windows that are not cycle skipped for inversion according to the criteria of similarity measured between the observed and predicted waveform within a given window. Through the iterations, the model improves and more data will automatically be assimilated into the inversion, forming a positive feedback of model update, and speed up the convergence rate. To provide additional constraints and also stabilise the inversion at the beginning, we include low-frequency surface waves and examine their contribution to the inversion. We validate the effectiveness of the PDA strategy in FWI through numerical experiments using the 1D linear gradient velocity model and the Foothill model. Compared with the conventional FWI strategy, the proposed PDA strategy in an elastic FWI can effectively mitigate the cycle-skipping problem and significantly accelerate the convergence rate. We further apply this method to the field data, and it improves the shallow part of the model with only a fraction of the entire dataset, demonstrating the great potential for practical usage.

KEYWORDS:

• Elastic full-waveform inversion
• cycle-skipping
• adjoint tomography
• progressive data assimilation

Acknowledgements

We thank the open-source spectral-element software package SPECFEM2D and Seisflows for our wavefield forward modelling and inversion. We appreciate the support from GeoTomo, allowing us to use the TomoPlus software package to conduct the data preprocessing and traveltime tomography. We also grateful for the open-source software “SeisFlows” developed by Modrak et al. (2018). The new features we have added to the SeisFlows is available through https://github.com/Jiangwb/seisflows-devel.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This research was supported by the Dedicated Fund for Marine Economic Development in Guangdong Province (Grant Number: GDNRC[2023]40), National Key Research and Development Program of China (No. 2022YFF0800701) and Jiangsu Provincial Department of Science and Technology (No. BE2022603). W.J. also thanks the financial support from Guangzhou Foundation Research Project (SL2022A04J00351) and Guangdong Basic and Applied Basic Research Foundation (2023A1515010898). We thank for the financial and data support from BGP Inc. through the project of the academician workstation.