Time‐damping Full Waveform Inversion of Multi‐dominant‐frequency Wavefields

The lack of low‐frequency components and the subsurface strong variations of velocity can lead to severe cycle‐skipping phenomenon, which is a big challenge to full waveform inversion of seismic data. Through the applications of the time‐damping and the time integration for decreasing the dominant‐frequency of seismic wavefield, a time‐damping full waveform inversion of multi‐dominant‐frequency wavefields is proposed. This method can efficiently eliminate the cycle‐skipping phenomenon. Velocity errors from shallow to deep can lead to misfits of travel‐time and their accumulations. The accurate inversion of shallow velocity can efficiently reduce the misfits of travel‐time and cycle‐skipping phenomenon in the inversion of later waveform. Applying the time‐damping approach to seismic data can obtain time‐damped data. The inversion of these time‐damped data with different damping values can produce the results from shallow to deep depth. The cycle‐skipping phenomenon is weak for the wavefields with lower dominant‐frequency compared to higher dominant‐frequency wavefields. The time integration of different orders of the seismic wavefield can produce wavefields with different dominant frequencies. The inversion results of low dominant‐frequency wavefields are used as the starting models for the full waveform inversion of high dominant‐frequency wavefields. Numerical tests using synthetic data lacking low‐frequency components below 4Hz of the 2D salt‐dome model have demonstrated the validity and feasibility of the proposed method. The final results show that the time‐damping full waveform inversion of multi‐dominant‐frequency wavefields has proper flexibility for seismic data lacking low‐frequency components and in case of strong subsurface velocity variations.