Automated velocity model building with wavepath tomography

Abstract

Wavefield-continuation migration generally is recognized as superior to Kirchhoff methods in complex velocity models, such as below rugose salt bodies. It accounts for multipathing, sharp velocity contrasts, and the limited bandwidth of seismic wave propagation. Wavepath tomography builds the velocity model in a way that is consistent with the wavefield-migration operator. Traveltime residuals are back-projected along a wavepath instead of rays. The actual wavefield-continuation operator is used to represent the wave propagation between surface source/receiver pairs and subsurface reflection points. A wavepath is obtained by multiplying impulse responses from a surface location and a reflection point. The inversion matrix is kept to a manageable size by restricting the wavepath to the first Fresnel zone. The considerable expense of computing a single wavepath kernel in comparison to ray tomography is partially offset by the smaller number of back projections necessary to sample the velocity model adequately. We have used wavepath tomography to build subsalt velocity models using 2D synthetic data. Wavepath tomography was implemented in 3D.