Improved estimation of P-wave velocity, S-wave velocity, and attenuation factor by iterative structural joint inversion of crosswell seismic data

We present an iterative joint inversion approach for improving the consistence of estimated P-wave velocity, Swave velocity and attenuation factor models. This type of inversion scheme links two ormore independent inversions using a joint constraint, which is constructed by the cross-gradient function in this paper. The primary advantages of this joint inversion strategy are: avoiding weighting for different datasets in conventional simultaneous joint inversion, flexible for incorporating prior information, and relatively easy to code.Wedemonstrate the algorithmwith two synthetic examples and two field datasets. The inversions for P- and S-wave velocity are based on ray traveltime tomography. The results of the first synthetic example showthat the iterative joint inversion take advantages of both P- and S-wave sensitivity to resolve their ambiguities aswell as improve structural similarity between P- and S-wave velocity models. In the second synthetic and field examples, joint inversion of P- and S-wave traveltimes results in an improved Vs velocity model that shows better structural correlation with the Vp model. More importantly, the resultant VP/VS ratio map has fewer artifacts and is better correlated for use in geological interpretation than the independent inversions. The second field example illustrates that the flexible joint inversion algorithmusing frequency-shift data gives a structurally improved attenuation factor map constrained by a prior VP tomogram.