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.