Viscoacoustic reverse time migration with stable and effective two-way attenuation compensation

Abstract

Intrinsic attenuation in seismic wave propagation leads to amplitude dissipation and phase dispersion in seismic data. The attenuation effect is a common cause for inaccurate image locations and dimmed image energy in reverse time migration (RTM). Conventional viscoacoustic or viscoelastic RTM (QRTM) methods implement attenuation compensation by reversing the sign of the amplitude loss term and keeping the dispersion term unchanged for both forward and backward wavefield extrapolation, which requires decoupled viscoacoustic wave equation and gives rise to numerical instability issue. To address these problems, we have developed a stable and effective two-way attenuation compensated viscoacoustic RTM method. The proposed method uses a new two-way normalized crosscorrelation imaging condition to compensate the attenuation effect. In the new imaging condition, only attenuated forward wavefield of sources and the viscoacoustic Green’s functions of receivers are required, which eliminates the instability source arising from the operation of reversing the sign of dissipation term in viscoacoustic wave equation. Since no modifications are made to viscoacoustic wave equation, the new imaging condition can be calculated without any additional computational cost and can be applied to both decoupled and coupled viscoacoustic wave equation-based RTMs, which is more flexible than other attenuation compensation strategies. Two synthetic tests and one field data example are presented to demonstrate the stability and effectiveness of the proposed method.