Angle-domain Migration Velocity Analysis using Wave-equation Reflection Traveltime Inversion

Abstract

SUMMARYThe main difficulty with an iterative waveform inversion is that it tends to get stuck in a local minima associated with the waveform misfit function. This is because the waveform misfit function is highly non-linear with respect to changes in the velocity model. To reduce this nonlinearity, we present a reflection traveltime tomography method based on the wave equation which enjoys a more quasi-linear relationship between the model and the data. A local crosscorrelation of the windowed downgoing direct wave and the upgoing reflection wave at the image point yields the lag time that maximizes the correlation. This lag time represents the reflection traveltime residual that is back-projected into the earth model to update the velocity in the same way as wave-equation transmission traveltime inversion. The residual movemout analysis in the angle-domain common image gathers provides a robust estimate of the depth residual which is converted to the reflection traveltime residual for the velocity inversion. We present numerical examples to demonstrate its efficiency in inverting seismic data for complex velocity model.

Shot- and angle-domain wave-equation traveltime inversion of reflection data: Theory

“…To eliminate the specification of reflection events in the data, Zhang et al (2011) present a modified extension of WT as wave-equation reflection traveltime inversion. Because the residual moveout analysis in the angle-domain CIGs provides a robust estimate of the depth residual, Zhang et al (2012) convert the depth residuals to the time lags and then invert them by the WT method. Al-Saleh and Jiao (2012) use a similar approach with the one-way wave equation.…”