基于波动方程转换的时间域多尺度全波形反演速度建模

To reduce cycle skipping of full-waveform inversion,a time-domain multi-scale full waveform inversion for velocity modeling based on wave equation transform is proposed.Velocity radiation patterns in different parameterized modes are studied,such as impedance-velocity and velocity-density.In the impedance-velocity parameterization mode,the velocity disturbance causes large-angle wave field disturbance; in the velocity-density parameterization mode,the velocity disturbance contributes equally for the wavefield disturbance at each angle.The impedance-velocity equation is used for low-wavenumber full-waveform inversion,to obtain a low-wavenumber velocity as the initial model to perform high-wavenumber full-waveform inversion.This method effectively avoids data transform in mixed-domain full waveform inversion and the Gibbs phenomenon in frequency-domain full waveform inversion.Meanwhile,the method fully exploits the advantages of time-domain full waveform inversion in calculation efficiency of numerical simulation and retains the characteristics of easy control of data matching in time-domain.A synthetic model was designed to compare and analyze the velocity gradient characteristics of the two kinds of parameterized models.The velocity building was realized by multi-scale full waveform inversion,from low-wavenumber velocity inversion using impedance-velocity equation to high-wavenumber velocity inversion using density-velocity equation.Tests on the Marmousi II model data showed that the proposed method could fully depict the fault shape and position,even if the initial velocity lacked low wavenumber components.